There is a typo in moveresize.c/clientMoveTile leading to one pixel gap between TILE_LEFT and TILE_UP_LEFT and between TILE_RIGHT and TILE_UP_RIGHT.
Created attachment 7554 Typo-in-clientMoveTile.patch
Adam Purkrt referenced this bugreport in commit 4ec48e8d52ad5afefb20d00345967a1bcf27a34f Typo in clientMoveTile https://git.xfce.org/xfce/xfwm4/commit?id=4ec48e8d52ad5afefb20d00345967a1bcf27a34f
Adam Purkrt referenced this bugreport in commit 020b0722b0d83e43ee295486ddffca504283f56a Typo in clientMoveTile https://git.xfce.org/xfce/xfwm4/commit?id=020b0722b0d83e43ee295486ddffca504283f56a