I suceeded to reproduce this issue with coLinux + UltraVNC on Win2000.

Yes, py3k claimed utf-8 error, so I tried trunk. Here is result.

*** event.keycode:  8
*** event.state:  0
*** event.char:  ''

*** event.keycode:  16
*** event.state:  4
*** event.char:  '\xc0\x80'

This '\xc0\x80' seems to be used in tcl as null byte '\0'. You can see
this magic value in tcl source and google.

I think we should convert this to '\x00' at python side. (shouldn't
treat this as utf-16)

I can see py3k + adhok.patch can output this result.

*** event.keycode:  8
*** event.state:  0
*** event.char:  ''

*** event.keycode:  16
*** event.state:  4
*** event.char:  '\x00'

Probably Tcl_GetUnicode does this conversion inside. (I'm not sure,
because I didn't look into source code so deeply) And I'm not sure why
this error doesn't happen with tk8.5.