This bug was tested only on Windows builds.
The behavior of this bug varies from quest to quest, yet produces consistent results once it occurs, and seems somehow related to the graphics data in the quest file.
Everything appears normal in ZQuest, the bug only manifests when playing the quest file in Zelda.exe.
Quests made in older builds seem to work normally until Extend is changed for a given entry in the "Graphics>Sprites>Link" menu in ZQuest. In one quest, the result was that the upper and lower halves of the sprite were fully swapped with each other; the bottom was on top, and the top was on bottom.
If the bug occurs on an existing quest, exporting a ZGP and importing it into another quest will carry over the specific results of the bug. (In the above case, the swapping of halves was preserved in the ZGP.)
Creating an entirely new quest and setting Extend on any of Link's sprites while also selecting a different tile will cause zelda.exe to animate with tiles that are not at all what was selected.