L750-59 of EditTrack was meant to remove duplicates, among other things. That it doesn't, means the bug is in L750-59.
The bug is not only about duplicating subfeatures if the same transcript is passed for merge. It can manifest itself in several ways as noted here https://github.com/yeban/afra/issues/82#issuecomment-68584897. This PR is ineffective against them.
fixes #82