It's starting to build and then claiming that the blocks it's placed are in it's way.

I found it, railcraft tracking blocks seemed to be the source.
As well as a phantom light block.

was able to double check it this time, reproduced without railcraft.

If a greenhouse is interupted in building, it uses up resources to start the building, and then demands enough resources to build the entire thing, and claims already placed blocks as obstructions.

i suspect your are comparing the block to the air block? you should call the isBlockAir() on the block or so so the fake blocks from RC and other mods are no longer in the way

And we also expect to greenhouses be able to continue the work, and not stop the process if go out of resources. Quite hard if you miscount 1 or 2 wood you have to dismantle all entire building and restart the process. Could you please take a bit deeper look into greenhouses? They're really annoying in this term.

So, railcraft invisible blocks cause the problem?