Sassalin,
I think it was a good idea to continue practicing until your vacation. Diving is something where you never stop learning. Repetition helps with these new skills and can make you more comfortable and competent in the water = greater enjoyment on your vacation.
Not too sure about separating you from the group. If your trusted buddy was not an instructor, then YOU should have evaluated if practicing in the deep end without an instructor was right for you. Maybe others can address if your buddy or the instructor working with a class had liability / responsibility for you.
Skills like mask clearing are important. From your post I gather you used a rental mask, and would assume that your vacation diving would not be in your own gear. The likelihood of a perfect fit on your rental mask on vacation is not high. This skill sounds like something you should continue to work on. Many people have difficulty with this initially, so dont worry.
Now, to play devil's advocate - If you are diving in Nassau and after 25 min at 50ft you laugh/sneeze/whatever and get water in your nose, what will you do? Is someone who stops you from bolting (here I mean a panicked ascent, probably faster than normal, with obvious breathing difficulty) in that situation someone who has rescued you or hurt you? I think anyone would agree that the answer is someone who has rescued you. If no one grabs you in that scenario what are the injuries that you could sustain? Not trying to be hard on you here, just want you to think it thru.
Knowing that you are practicing skills for real life diving reasons, should another persons response be a proper safety reaction or should they let it pass and HOPE you do it right when it really counts? Yes, I'll agree that it sounds like it was rough and the first thing you could have heard was 'catch your breath, relax, then we will talk about what you did wrong' and you didn't.
My dive buddy that I went thru initial certification with was very worried about sneezing fits that he gets from time to time. He asked the instructor. Her response was - 'work it out, dont bolt to the surface'. She also told me that when we go diving that I should watch out for this and not let him bolt. The first time he started sneezing while diving, he signalled me to swim closer beforehand, i saw him sneeze a few times, he worked thru it and gave the ok signal and continued diving. Now he doesn't even bother to get my attention because he KNOWS he can work thru that problem.
If you still have concern about whether this was the right thing to do or not, go into a few different dive shops and ask them if they let students bolt to the surface when they panic.
I hope none of that sounded harsh. I think you missed an opportunity to learn how to work thru an issue. However i think you learned something that you could have trouble with - not a bad thing to know so that you can work on it. I know you cant simulate this experience easily, but you can work on making sure your problem solving skills are second nature.
Keep working at those mask clears and enjoy your trip to Nassau.