I have Dredgeworks and Ocean Dumping. This might be an unintended interaction between them. Ocean dumping allows me to treat oceans like lava, voiding things. Land drills will stop because the spot is full. Floating drills from DW dump into the ocean, which might normally stop them (I'm not sure, I just added DW) but they're just going because of OD.

Since the drill places mined ore on the ground, it goes through the same item disposal logic as an inserter dropping items or a player dropping an item with the Z key. So I'd consider this expected behavior rather than an unintended interaction between the two mods.