For some reason, the game currently assumes that if you miss your swing while mining, you meant to destroy the nearest spike, team tunnel, or stone door. It's extremely frustrating and I've seen the killing blow to a tunnel be an accidental swing by a builder. It doesn't matter if these "special" blocks are behind you when you miss; they're getting the axe. To add injury to injury, the dynamic blocks susceptible to this behavior are generally the most expensive. So basically, if my cursor isn't on something, or at the very least, if I'm facing away from it, I'm not trying to mine it, and the game shouldn't assume I am.