Yep, you appear to have found a bug. On Windows if I set the stripboard size to 36/21 and set board size, the strip board expands incorrectly (the expansion isn’t strips as the original was) and when I drag a Raspberry PI cpu in from core, moving it around slows right down as you describe. Deleting the perf board brings speed back up to normal. One more for my long list of bugs to have a bash at 
. Looks to be only the strip board, the perf board (which is what I usually use) appears to work fine.
Peter