hoes can't till when some plant nearby, like flowers and saplings from BOP or tomatoes from Farmer's Delight.
The sound of tilling will be played, and the durability of hoes will be reduced, but the farmland will not appear correctly.
Seems to be related to the right-click harvest area of hoes.

Appears to occur around rice crops as well.

This should be fixed with the latest quark so it should be fixed in the next bliss update too