The speed increase adds difficulty by causing you to pick up debuffs by accident.
The solid blocks original were not destructable. I had to change this because of tanks getting stuck in solid blocks. I used this as a work around to the blocks spawning inproperly sometimes. (A bit of a hidden mechanic.)
The other bug of blocks sometimes switching back to solid is due to differences in power level vs remaining block hp. I think it's a logic error somewhere in if checks.