I'm happy to announce that RT 4.0.10 is now available.
This release contains several bugfixes and a fix for a regression introduced in 4.0.9. If you have a Queue configured so that users have SeeQueue and CreateTicket but not ShowTicket (they can create tickets, but won't be able to see them after creation) then any Custom Fields assigned to that Queue and filled in during creation would be lost during submission.
A complete changelog is available.