Dispensers will not fire pumpkins

A dispenser automated with a redstone comparator clock will shoot a variety of items, including jack o'lanterns, but will not fire pumpkins (as dropped items). Clock continues to run because of the pumpkins remaining in the dispenser's inventory, but only smoke comes out unless a different item is added. Found the bug on multiplayer and duplicated it in single player. Used a chest and hopper above the dispenser to feed pumpkins into it (which worked fine) but the pumpkins do not leave the dispenser.

Also tried to activate a dispenser with pumpkins using a lever - still nothing.

Again, other items fire, just not pumpkins.

Thanks!!