Generally Trojans can't be repaired as it isn't an infected file and I wouldn't have thought that the Repair button would be live (allow the option).
I think the Repair buttom is always live (not greyed), but it works only when it's possible to use the VRDB
So it would appear that the FP on an existing exe file that may possibly have been scanned by the VRDB (?) may allow the repair option to be attempted.
A false positive, a real virus or any other unrepairable virus. I think Repair will be always there. Works only when it's possible.
That would explain why it would appear the repair completed with success as it hadn't changed (been infected).
This is the strange part... I mean, the repair being completed...
Being an FP detection could also explain why it would be detected again even after repair.
Again, my opinion is that this is not related with a false positive or real infection. Being detected again is due to the virus behavior (mutating, changing, appearing in other files, reinfecting, etc.) and the avast! detection but not with being a false positive.
A false positive could be detected just once... repaired, deleted, etc. and does not appear anymore.
The strange, again, is a sucesfull repair...