http://bugs.winehq.org/show_bug.cgi?id=26841
--- Comment #11 from David Hedberg david.hedberg@gmail.com 2011-05-27 16:27:16 CDT --- The file extension handling in the new dialogs has been improved in wine 1.3.21, which should take care of this bug.
The custom controls (checkboxes etc.) added to the dialogs by reaper should also show up now and basically be usable, with some small glitches remaining.