If I make a modifier, no matter what the drop-downs are set to, clicking "add" adds a slot->slot type.
This means I can't choose TE or liquid filters, and I can't remove things from the scan.

Seperate issues to avoid spamming: there doesn't seem to be any way to add liquid blocks to a filter, and any filter will not match liquid blocks in the scanner

Show me a screenshot of what you're trying to do?

No Matter what those two boxes say, the add creates a slot -> slot

Edit: in case it matters, this is minecraft 1.12

And version of rftools?

Also what if you actually put a liquid in the slot before pressing add?

I'm using the FTB Direwolf20 1.12 pack. It has version 7.15 of rftools.

How do you put a liquid into the slot? A bucket does not work

Edit: forcibly updated the version in the pack to the latest on twitch, and updated dependencies.
this is still an issue on that version

Um it should. What happens if you try to put in a bucket?

It creates a slot->slot with the bucket on the left, which never matches any blocks.
Note that this is an issue with the other settings (TE,Ore, and Void) as well

Hmm ok you are right. This got broken somehow. I'll fix

Ok, stupid error. Will be fixed next release