Hanging items can't quite be rolled back because of a bukkit bug with their facing directions. https://bukkit.atlassian.net/browse/BUKKIT-3371
Hanging Entity Breaks for items like tnt, tntminecarts, fireballs, lightning, and wither skulls do not trigger an event we can track. https://bukkit.atlassian.net/browse/BUKKIT-3943
Item frame rotation can't be properly tracked because Bukkit doesn't fire any interact events for them. https://bukkit.atlassian.net/browse/BUKKIT-3402
Free-standing signs may rollback facing an exact direction when it was placed with an orientation between two directions.
Blocks that form from lava/water mixing are extremely difficult to track properly because bukkit has no proper events for them. We've begun work a custom tracking system but it's difficult work.
Restoring block-place actions for blocks with orientations (furnaces, pistons, etc) won't retain the orientation because there are some problems with how Bukkit/MC fire the event versus set the orientation. https://snowy-evening.com/issues/details/479/248/
Shift+clicking items into a furnace do not report a usable slot, so we can't properly know which furnace slot was used if you activate an a:insert restore.
When one side of a double chest is broken, we can't properly record the slots of items in the other side because it turns into it's own single chest. While we can restore items to slots in each chest, some slots lose meaning when the chest becomes double after a rollback.