Similar to steel destruction in L1, a miner can take one strike out of a one-way-up wall (before the one-way-up terrain stops him from continuing as a miner).
Happens in both stable and experimental. Does not happen with bashers or diggers. Have not yet tested other directions of one-way wall (whether with miners or other skills).
Have tested more thoroughly, and the results is that it's exclusive to miners + one-way-up. However, it does not matter whether the miner is facing left or right.
And, fixed for next update.