I’ve noticed when copying geometry from one block to another, the Block Edit window disappears, explodes the block and locks everything else. So it’s then necessary to redefine the Block, then unlock all the visibilities. This is incredibly annoying.
A way around is to copy from one block, paste into the overall model, cut, then paste into the other block. It’s difficult to remember to do this every time.
I can’t think of a functional reason for it to be this way.