this is in 0.12 branch, right?

Yes. It's svn revision 537042. 

The latest svn revision (537289) shows a differnet behaviour: 
Set the testbed account to "Online", then choose "Show my own webcam". Now the account is not set to "Offline" anymore, a window that should show the webcam image opens. But it does not show the webcam image, it shows something like "No webcam image received." (this is not what it says, I translated it, as I use the German localization). 
It's probably not due to my webcam (also there are strange values in konsole ouptut), as it works fine with MSN and Yahoo!. 

Here is the konsole ouput: 

kopete: [void TestbedAccount::slotGoOnline()]
kopete: [virtual void TestbedAccount::connect(const Kopete::OnlineStatus&)]
kopete: [void KopeteWindow::slotAccountStatusIconChanged(Kopete::Contact*)] [variant:  toString=]
kopete: [void KopeteWindow::slotAccountStatusIconChanged(Kopete::Contact*)] [variant:  toString=]
kopete: [void KopeteWindow::slotAccountStatusIconChanged(Kopete::Contact*)] [variant:  toString=]
kopete: [void TestbedAccount::slotShowVideo()]
kopete: [int Kopete::AV::VideoDevicePool::open()] open(): Device out of scope (1752379187). Defaulting to the first one.
kopete: [int Kopete::AV::VideoDevice::open()] called
kopete: [int Kopete::AV::VideoDevice::open()] File /dev/video0 was opened successfuly
kopete: [int Kopete::AV::VideoDevice::checkDevice()] checkDevice() called.
kopete: [int Kopete::AV::VideoDevice::checkDevice()] checkDevice(): /dev/video0 is not a V4L2 device.
kopete: [int Kopete::AV::VideoDevice::checkDevice()] checkDevice(): /dev/video0 Trying V4L API.
kopete: [int Kopete::AV::VideoDevice::checkDevice()] /dev/video0 is a V4L device.
kopete: [Kopete::AV::VideoInput::VideoInput()] Executing Video Input's constructor!!!
kopete: [Kopete::AV::VideoInput::VideoInput()] Executing Video Input's constructor!!!
kopete: [int Kopete::AV::VideoDevice::checkDevice()] checkDevice(): Supported pixel formats:
kopete: [int Kopete::AV::VideoDevice::checkDevice()] checkDevice(): 16-bit RGB565
kopete: [int Kopete::AV::VideoDevice::checkDevice()] checkDevice(): 24-bit RGB24
kopete: [int Kopete::AV::VideoDevice::checkDevice()] checkDevice(): 32-bit RGB32
kopete: [int Kopete::AV::VideoDevice::checkDevice()] checkDevice() exited successfuly.
kopete: [int Kopete::AV::VideoDevice::initDevice()] initDevice() started
kopete: [int Kopete::AV::VideoDevice::initDevice()]     Streaming interface
kopete: [int Kopete::AV::VideoDevice::showDeviceCapabilities()] showDeviceCapabilities() called.
kopete: [int Kopete::AV::VideoDevice::showDeviceCapabilities()] Card model: Z-star Vimicro zc0301p
kopete: [int Kopete::AV::VideoDevice::showDeviceCapabilities()] Card name : Z-star Vimicro zc0301p
kopete: [int Kopete::AV::VideoDevice::showDeviceCapabilities()] Capabilities:
kopete: [int Kopete::AV::VideoDevice::showDeviceCapabilities()]     Video capture
kopete: [int Kopete::AV::VideoDevice::showDeviceCapabilities()]         Read
kopete: [int Kopete::AV::VideoDevice::showDeviceCapabilities()]     Max res: 640 x 480
kopete: [int Kopete::AV::VideoDevice::showDeviceCapabilities()]     Min res: 176 x 144
kopete: [int Kopete::AV::VideoDevice::showDeviceCapabilities()]     Inputs : 1
kopete: [int Kopete::AV::VideoDevice::showDeviceCapabilities()] Input 0: ZC301-2 (tuner: 0)
kopete: [int Kopete::AV::VideoDevice::showDeviceCapabilities()] showDeviceCapabilities() exited successfuly.
kopete: [int Kopete::AV::VideoDevice::initDevice()] initDevice() exited successfuly
kopete: [int Kopete::AV::VideoDevice::selectInput(int)] Selected input 0 (ZC301-2)
kopete: [float Kopete::AV::VideoDevice::setBrightness(float)]  called.
kopete: [float Kopete::AV::VideoDevice::setContrast(float)]  called.
kopete: [float Kopete::AV::VideoDevice::setSaturation(float)]  called.
kopete: [float Kopete::AV::VideoDevice::setWhiteness(float)]  called.
kopete: [float Kopete::AV::VideoDevice::setHue(float)]  called.
kopete: [int Kopete::AV::VideoDevice::open()] exited successfuly
kopete: [void Kopete::AV::VideoDevicePool::loadConfig()] called
kopete: [void Kopete::AV::VideoDevicePool::loadConfig()] Current device: Model Z-star Vimicro zc0301p Device 0
kopete: [void Kopete::AV::VideoDevicePool::loadConfig()] Device name: Z-star Vimicro zc0301p
kopete: [void Kopete::AV::VideoDevicePool::loadConfig()] Device current input: 0
kopete: [bool Kopete::AV::VideoDevice::setWorkaroundBrokenDriver(bool)] VideoDevice::setWorkaroundBrokenDriver(false) called.
kopete: [int Kopete::AV::VideoDevice::selectInput(int)] Selected input 0 (ZC301-2)
kopete: [float Kopete::AV::VideoDevice::setBrightness(float)]  called.
kopete: [float Kopete::AV::VideoDevice::setContrast(float)]  called.
kopete: [float Kopete::AV::VideoDevice::setSaturation(float)]  called.
kopete: [float Kopete::AV::VideoDevice::setWhiteness(float)]  called.
kopete: [float Kopete::AV::VideoDevice::setHue(float)]  called.
kopete: [float Kopete::AV::VideoDevice::setBrightness(float)]  called.
kopete: [float Kopete::AV::VideoDevice::setContrast(float)]  called.
kopete: [float Kopete::AV::VideoDevice::setSaturation(float)]  called.
kopete: [float Kopete::AV::VideoDevice::setHue(float)]  called.
kopete: [bool Kopete::AV::VideoDevice::setAutoBrightnessContrast(bool)] VideoDevice::setAutoBrightnessContrast(false) called.
kopete: [bool Kopete::AV::VideoDevice::setAutoColorCorrection(bool)] VideoDevice::setAutoColorCorrection(false) called.
kopete: [bool Kopete::AV::VideoDevice::setImageAsMirror(bool)] VideoDevice::setImageAsMirror(false) called.
kopete: [void Kopete::AV::VideoDevicePool::loadConfig()] Brightness:0.5
kopete: [void Kopete::AV::VideoDevicePool::loadConfig()] Contrast  :0.5
kopete: [void Kopete::AV::VideoDevicePool::loadConfig()] Saturation:0
kopete: [void Kopete::AV::VideoDevicePool::loadConfig()] Whiteness :0.5
kopete: [void Kopete::AV::VideoDevicePool::loadConfig()] Hue       :0.5
kopete: [void Kopete::AV::VideoDevicePool::loadConfig()] AutoBrightnessContrast:false
kopete: [void Kopete::AV::VideoDevicePool::loadConfig()] AutoColorCorrection   :false
kopete: [void Kopete::AV::VideoDevicePool::loadConfig()] ImageAsMirror         :false
kopete: [int Kopete::AV::VideoDevicePool::open()] Number of clients: 1
kopete: [int Kopete::AV::VideoDevice::setSize(int, int)] setSize(320, 240) called.
kopete: [int Kopete::AV::VideoDevice::setSize(int, int)] Card doesn't seem to support YUV420P format. Trying RGB24.
kopete: ------------- width: 1112777984 Height: 1104707912 Clipcount: -1074732488 -----------------
kopete: ------------- width: 320 Height: 240 Clipcount: 0 -----------------
kopete: ------------------------- ------- -- m_buffer_size: 230400 !!! -- ------- -----------------------------------------
kopete: [int Kopete::AV::VideoDevice::initRead()] called.
kopete: [int Kopete::AV::VideoDevice::initRead()] m_buffer_size: 230400
kopete: [int Kopete::AV::VideoDevice::initRead()] exited successfuly.
kopete: [int Kopete::AV::VideoDevice::setSize(int, int)] setSize(320, 240) exited successfuly.
kopete: [int Kopete::AV::VideoDevicePool::startCapturing()] startCapturing() called.
kopete: [int Kopete::AV::VideoDevice::startCapturing()] called.
kopete: [int Kopete::AV::VideoDevice::startCapturing()] exited successfuly.
kopete: [virtual TestbedWebcamDialog::~TestbedWebcamDialog()]
kopete: [int Kopete::AV::VideoDevice::stopCapturing()] called.
kopete: [int Kopete::AV::VideoDevice::stopCapturing()] exited successfuly.
kopete: [int Kopete::AV::VideoDevice::close()]  called.
kopete: [int Kopete::AV::VideoDevice::close()]  Device is open. Trying to properly shutdown the device.
kopete: [int Kopete::AV::VideoDevice::stopCapturing()] called.
kopete: [int Kopete::AV::VideoDevice::stopCapturing()] exited successfuly.
kopete: [int Kopete::AV::VideoDevice::close()] ::close() returns 0

Could you please try the latest version? I have changed a bit that code, so it might be working now.

I tried the latest version, it works now. Thanks. 

*** Bug has been marked as fixed ***.