Solid tiles forced into open doors become invisible and drop nothing when door is closed

I've run into an issue where in trying to automatically harvest dirt (that's being heated from slime) on conveyor rails using doors (something I thought worked for harvesting falling sand or regolith tiles), the dirt is spawning in a stack above my tiles (when the one conveyor rail tile is full) invisible within the open doors and I can't get any resources out of it, even though it raises the items that should otherwise be sitting on the ground beneath the open doors. You can see a null zone in the oxygen overlay where a solid is supposed to be. 

I've monitored the piles of dirt within the doors and to the left of them and neither changes sizes upon deletion of a hidden tile.

The way this setup works for what it's worth:
->slime generated by morbs+pufts
-> sent to conveyor rail
-> rail passes through solid blocks until reaching a hot room with "thermal gates" or whatever smarter people call them that go: room to be heated - metal tiles -  door controlled by temp sensor - metal tiles - heat source
-> slime on rail converts to a small amount of dirt
-> if tile where conversion happens is already occupied, stack the dirt on top in the nearest "airspace"
-> repeat, hopefully digging up the dirt so it doesn't create an infinite stack into space