I have recently upgraded to 2.14.11 from 2.8.2. I opened an old project which hasn't been opened since before I upgraded and came across an issue.
I started editing a vector layer which was already present in the project (i.e. not a new layer), created a new polygon and then went into the attributes table to enter the information. I then noticed that there were two rows for the single polygon I had created, and that you couldn't select one without selecting the other.
When I attempted to copy the polygon and then delete the original one causing the issue, one of the original 2 rows was deleted but the second gave the error 'Problem deleting feature'.
Has anyone else had this problem and is it an artefact of moving from 2.8.2 to 2.14.11. I haven't had this problem with any of my other projects from 2.8.2 that I have opened, but I think that I have been creating new layers in them instead of amending old ones.