That's a shame! Glass is funny like that. You could take two pieces that look completely the same,
throw one as hard as you can on concrete and it wont break, and the other will break falling a few inches onto carpet.
The fact that IBtanks don't have flame polished ends could possibly contribute to them being more fragile than they would be otherwise. While ground down quite nice (pretty similar to ground glass joints on scientific labware) it still leaves a bunch of tiny tiny cracks on the end of the tube, that are a great starting place for a break to happen when too much stress is applied.
I've dropped my IBtanks several times on concrete pretty hard with zero damage. Then one of them simply tipped over on my coffee table, and it chipped a piece off the end. Which seems ridiculous as you'd imagine the large falls onto concrete would have broken them, but a tiny soft tip-over on a coffee table breaks it. Glass is just an inconsistent material.
Luckily replacement glass tubes are dirt cheap from IBtanked.