From a 7.5 year old news posting (with a reply by Kevin Hugo speaking
on behalf of slash'em...): when a monster "nimbly jumps to evade" hero's
kick, it can pass through walls and grid bugs can jump off their grid.
Likewise when a joust or staggering blow knocks a monster back, it could
move grid bugs diagonally. This fixes both cases.
Offhand I can't think of any other non-standard movement situations
which might need similar handling, but it wouldn't surprise me if there
are some. Leashed movement is close but I don't think maybe_mnexto helps.