T500 Keyboard types garbage characters

Question

I've seen this problem occasionally both on Vista and now on Windows 7 (64-bit) - now and then when I type on the keyboard I get garbage characters on the screen.  The characters seem to appear in ASCII-code order, for example if I type 'http' I might see '1234'  or some other 4-character sequence, in order.  This has happened in Thunderbird, and goes away after a while.  It isn't specific to Thunderbird, if I'm in the 'garbage character' mode and open a Notepad window, for example, it will also display incorrect characters.  After closing a few things and re-opening, it eventually clears up (I'm not sure about the exact sequence that corrects it).
I've searched this forum and other places but not seen any references to a similar problem.   Any ideas would be welcome!

Answer 1

This problem is still happening, occasionally and randomly.  For example, just before typing this post (which is working normally, it seems), I was using another app and had the problem.  I opened Notepad, and typed "jjjjjjjjj", repeatedly, and this is what appeared on the screen:
qwertyuiop[]asdfghjkl;'`\zxcvbnm,./-+\1234567890-=
and would repeat if I continued to type any letters at all (didn't matter if it was "j" or any other letter, the same sequence appeared).  Then, I switched to the Spanish keyboard, and tried the same thing and saw:
qwertyuiop´+asdfghjklñ{|}zxcvbnm,.--+<1234567890'¿
Again, it would repeat endlessly as long as I kept typing something.
The shift key would produce the corresponding capital or shifted characters (i.e. "%" instead of "5").
It clears up spontaneously, but is rather annoying when it happens.
It is not caps-lock or num-lock related, nor apparently multiple-language-keyboard related.
Any clues???
Thanks!