I have a back problem, the bones can sort of easily 'dislocate', if you can call it that. The back of the shoulders are included with my back problem. I wonder if it's safe to continue doing dips.
NEVER perform a movement that feels unnatural, especially if you have medical issues. I am not a fan of these types of dips to begin with due to the fact that A LOT of undue stree is placed on the whole shoulder, so I would definately get rid of these and include more efficient movements in your workouts for your triceps. Hope this helps and good luck.