Deleting branches

I am investigating Gitlab and probably best to do any dumb mistakes before doing it on a live system.
So I created an issue, and made a new branch via the new branch button. I then decided to delete the branch from the command line in the git repo (git branch -D).
Now when I open the issue in gitlab, I get a 500 error. How do I recover from this?
Also, when making a new branch in an issue, can I decide where it should branch from. If I create a new branch from the branches screen then I can but from an issue, it appears to branch from master.

This can be closed as have opened “Gitlab created branch deleted via git, now issue is 500”