Sorry man--not your day apparently. Did you chew out the store owner for falsely accusing you later? As far as the LEO, I'm not sure if he did anything wrong, but he should have given you back your round, I agree. Did you ask him for it? He probably just forgot about it with everything else going on...
Also, I know it's 20/20 hindsight, but...why not just try on the shorts instead of worrying about your pant's size? I go in dressing rooms every now and I just drop my pants with my weapon still holstered, try on the new clothes, and then get dressed again. I will say that one thing I love about my Galco Summer Comfort is that I can just snap off the holster without removing my belt...hope you have better luck nextime! At least you kept your cool--some guys would have reacted differently and perhaps got in some trouble.