I just tried it on another N900. It is running a slightly older firmware. I think it's PR1.2, mine has PR1.3 + CSSU. The other N900 has the same problems.

Would you be willing to run some code on yours?

http://pastebin.com/ke06n2Nc

Put that in a file called test.tcl in your N900 and run it:

$ wish8.5 ./test.tcl

Then please tell me if you can type any capital letters, numbers, symbols or even enter a new line. Please note that the letter 'x' closes the app.

Please let me know.