weird tab self insert behavior on windows -- how can I fix?

[fork]

Here is my version:

GNU Emacs 24.0.50.1 (i386-mingw-nt5.1.2600) of 2011-01-17

Sometimes (but not always) when I set tab to self-insert, I get a funky
character inserted (a square with 3c9296 in it) whenever I hit tab.  Sometimes
it works fine.

Has anybody seen this behavior, and know how to fix it?

I am happy to use a newer test binary, though I always have a hard time finding
them.

Tx