Bug 187410

This doesn't sound like a KDE issue. Can you try asking at Ubuntu-Forums, specifying your Ubuntu and Kernel versions, and your Keyboard model ?

That is not entirely truth. I took some time trying to reproduce the bug, and here's what I've found:

I've got Logitech S 510, but it should work for any USB keyboard, or at least cordless keyboards with USB receiver. Turn Num Lock on, unplug the keyboard/receiver, plug it again. The led is off although Num Pad works.

Outside KDE it's slightly different: switch to terminal with ctrl+alt+f1 and log in. Do all the steps to reproduce this bug. After the keyboard is pluged again Num Lock is off. Pressing Num Lock key now disables Num Pad, pressing it again enables both, Pad and LED and everything is back to normal.

Have you tried "Pressing Num Lock key now disables Num Pad, pressing it
again enables both, Pad and LED and everything is back to normal." (the last steps of your outside-KDE description) inside KDE ? Do you get the same result? Sorry to ask but I didn't understood properly.
Thanks

Ok, I'll try to explain it more clearly:

INSIDE KDE
1. NumLock led is on, NumPad works,
2. Unplug keyboard and plug it again,
3. NumLock led is off, NumPad works,
4. Press NumLock key,
5. NumLock led is on, NumPad doesn't work,
6. Press NumLock key again,
7. NumLock led is off, NumPad works,
8. Press NumLock key again,
9. NumLock led is on, NumPad doesn't work,
10. ...

OUTSIDE KDE
1. NumLock led is on, NumPad works,
2. Unplug keyboard and plug it again,
3. NumLock led is off, NumPad works,
4. Press NumLock key,
5. NumLock led is off, NumPad doesn't work,
6. Press NumLock key again,
7. NumLock led is on, NumPad works,
8. Press NumLock key again,
9. NumLock led is off, NumPad doesn't work,
10. ...

Thanks for the explanation

I have the same issue, but I don't need to unplug the keyboard at all. I'm using a desktop computer in suse with a standard PS/2 keyboard, and this only happened to me with KDE 4.2.2 (KDE 3 was fine)

I don't know exactly how it happened, maybe sometimes after entering the password to unlock the screensaver. I'm not sure, I will try to find out how to reproduce it. It happened to me several times.

Anyway, I think it's not related to unplugging the keyboard.

*** Bug 197351 has been marked as a duplicate of this bug. ***

This is my version of the occurance:

When NumLock on KDE startup is set to Turn on in Keyboard & Mouse in System
settings, NumLock turns on but not its LED on keyboard. This results in a
reversely behaving (NumPad is enabled when LED is off, disabled when on)
NumLock and happens consistently.

Expected behaviour:
NumLock LED should turn on when NumLock is turned on on KDE startup
Num pad should work when NumLock LED is on
Num pad should perform other functions (home, end, arrows and such) when LED is
off.

How to reproduce:
1- Go to system settings
2- Open keyboard and mouse
3- Select Turn on under NumLock on KDE startup section under Keybard tab.
4- Restart computer (I don't know if restarting KDE or logging off and on will
reproduce it)
5- Viola! You have an inversely behaving NumLock LED.

Notes:
- Keyboard is a Microsoft Ergonomic Keyboard 4000 USB but reproduced in an HP
laptop and other USB keybards successfully.
- Bug is present since 3.5.9 days.
- Bug disappears in virtual terminals (VTs).

Also have this problem.

Keyboard Microsoft Comfort Curve 2000, Debian Testing, KDE 4.2.2.

This bug still happens in KDE 4.2.4, Debian Testing/Sid.

Keyboard IBM-6326

*** This bug has been marked as a duplicate of bug 183308 ***