At the corner of a room an actor can walk through/in the wall. That is because all walkboxes are square at the moment.
In addition to the z-depth (0-3) a walkbox mask contains two special flags for cornered walkboxes.
If mask & 0x88 is true the walkbox must be triangulated. Another bit (mask & 0x04) determines if the mask belongs to the left or right corner of a room.
Note that ladders (and the man-eating plant) seem to always have a walkbox mask of 0x8A. I'm not sure if those walkboxes have to be triangulated too.
At least a z-depth of 2 might be plausible.
Ticket imported from: #2856940. Ticket imported from: patches/1187.
Thanks, I added the patch to ScummVM SVN.