Known Issues in fx3.1b3 release notes says "If you are using MS Natural Input 2002 v8.1, IME will automatically activate when certain text fields are focused. This is a known Microsoft issue (see bug 478882)." But bug 478882 is only on trunk and it isn't on branch. So it should not be in this release notes.
https://www-trunk.stage.mozilla.com/en-US/firefox/3.5b4/releasenotes/ also has the known issue about bug 478882, but it should not.
fixed on trunk Sending 3.5b4/releasenotes/index.html Committed revision 24941.
-> v. Thank you!