The recent changes in SpecialUpload.php in revision 32077 have made the wpDestFileWarningAck hidden input disappear. I don't know if that isn't needed anymore, but in any case this generates a Javascript error in /skins-1.5/common/upload.js, line 102.
And while we're at it, line 99 of upload.js is missing a ';'. Instead of
if ( warning == '' || warning == ' ' ) {
it should read
if ( warning == '' || warning == ' ' ) {
Version: unspecified
Severity: normal