In apps that may use multiple instances of the Konsole KPart, such as the KDE 4 version of KDevelop or the WIP port of Yakuake, only the first instance will actually work. The second instance will not react to showShellInDir(), i.e. it will not produce a shell. Typing into it spews "Pty::doSendJobs - Could not send input data to terminal process." onto stdout. CC'ing apaku who reproduced it for me in KDevelop 4.
This was a simple silly bug in the KPart. Should be fixed by SVN revision #754194 Please reply if there are still any problems.
There was a mistake in the aforementioned commit, please use SVN revision #754203 or later.