Add more options other than "Marked Fixed" in Collaborator. Marked Fixed can be confusing. Options: Mark Fixed Mark Closed Concur with Reject Concur Withdrawal
I personally don't think we need so many options, but we do need to distinguish between a "fixed" defect and a "withdrawn" defect. Right now the only ways to withdraw a defect is to it mark it fixed (which is misleading, and also bad for auditing and reporting) or delete it (after which, if it turns out that the defect was valid, it can't be restored.. a new defect has to be created).
If there is a way to undelete a deleted defect that would be a suitable workaround IMO.