Git plugin fails to delete 'not fully merged' branch

We are using a topic-branch model in which we do lots of rebases. When the topic branches are completed, some of them end up in a not fully merged state, but are deleted from the server anyway.

When the git client tries to delete the branch it is getting an error due to the use of the "git branch -d" command to remove the branch.

Using "git branch -D" would force the removal of the local branch, which should be done anyway because the Fisheye is just a reflection of the repository as it is.