I had a tarfful way back when that had a broken spring like that.
Interesting. Especially since a friend of mine has a Tarfull that broke as well.
I personally have a theory that it does it because of the way the arm in certain strikers are designed. With lightsabers, maces, sais, and chains, the striking surface or the arm holding the striking surface is thin enough to bend when the striker is fully wound up, alleviating a large amount of the stress on the figure's glue. With Beast, Tarfull, and Doc Ock, their arms/tentacles are much thicker and don't have as much give. This would put more pressure on the glue inside the figure leaving to an inevitable break.
Again, this is just a theory. If a bunch more people come in here and claim to have busted other "thick-armed" strikers then it might have more proof for its truth.
"All in all, a most unpleasant fellow." - Obi-Wan's candid thoughts on General Grievous
Grievous - you might be pulling back on Beast too hard... I've had a couple Kit Fistos and S3 Kenobis end up the same way as your Beasts... they just spin round and round. I pulled back on them too hard and it caused them to break.
I also had this happen to a S1 Chewbacca, but luckily I jimmied with it a while and he works again, only he strikes backwards now (so instead of a paw strike he has a backhand slap)!
"It's all about the whites" - Greyelephant (Tixcon 2008)
I don't buy too many boosters (what with a wife and now a house!), but out of those I have bought I ended up with a total of 4 Beasts. All of them work superbly. In fact, I've never had an Attacktix break on me, and out of hundreds of Attacktix in my collection, only one of them was bought defective. I agree with Greyelephant - I think you're too beastly on them!