^That sucks about getting robbed bro.
Slipping out of a vein isn't really uncommon. Many people (including myself) pull back a tiny bit once or even twice sometimes during the shot to see if I haven't slipped out.
If you're using big veins like the ones in the crooks of your arms slipping out almost never happens, but if you're using smaller veins (because better ones have collapsed or simply because you are rotating and giving the big veins a chance to heal), slipping out isn't at all uncommon. Depends on how steady your hand is I guess, but it can happen to the best of us. Checking if you're still registered during your shot is the only way I know of to make sure you're still in the vein if you're injecting in smaller or rolling veins.
@whosa: you didn't waste the H, it'll still work. It'll take a while longer to come up, and might not be as strong as if you had injected in the vein, but it'll definitely still work. It doesn't just 'disappear' if you shoot it next to a vein. It gets absorbed more slowly. If it was in muscle tissue the BA is still 100%, if it was just below the skin (sc) I don't really know the BA, and I can't really find a decisive answer on google, most say it's between 50-70%. So it's a little bit of a waste, but not completely lost.
OT: Just shot an oxy 80. About to roll a spliff of some hash I thought I'd lost but just found back. I always like it when that happens.