Dr. Riboh: A Common Shoulder Injury in Swimmers 

So there's levels of dislocated and not.... Explains a lot.

Does this also happen with breast stroke swimming? I have pain in my upper arms when doing a lot of training, mostly in one arm alternating = when reaching high over head I feel a sharp pain ..... when stopping with training due to other health problems the pain goes away .... my swimming trainer does not find any source for this pain and doctor could not explain / find the source for the problem :-((( Thus, I am totally surprised by your description ;-)

I am a swimmer