Could have also been a bad bevel on the needle itself. Did you notice it was hard to get it through the stopper when you did your draw? I ask because about 10 years ago I was giving a buddy his shot. It was hard to get through the stopper and I kept trying to hit his glute and it just wouldn't go in. Finally I looked at the needle and it didn't have a bevel in it. I was basically trying to jam a 22 gauge metal straw in his ass.

Might not have been the case but something to check out next time.