If the screen jumps or flashes during a block opertaion you are probably still using version 1.0 of the WordStar Command Emulator. In that version, when you used Copy, Move, or Delete on a block marked with ^KB and ^KK Word had to go and select (highlight) the block before carrying out the operation. This is the jumping you see.
Version 1.1 changes the way that the WordStar block operations work, which has stopped the jumping (except for ^PK as Word still needs to physically select the block for printing). If you are still using version 1.0 you should purchase an upgrade.