Quark trap doors, such as the jungle trapdoor, act as a ladder piece when used with vanilla ladders, but not when used with iron ladders from Quark. I don't think this behavior is intended.

My temporary workaround.

(https://user-images.githubusercontent.com/7505105/34636332-787e34a8-f264-11e7-9d8b-0baa902e528b.png)

Unfortunately due to vanilla code being vanilla code, I can't fix this without intrusive patches, sorry.

You can't modify the behavior of blocks added by Quark without modifying vanilla code? That seems odd.

Jaded Trapdoors from OpenBlocks work with your iron ladders just fine, but perhaps they are using intrusive code.

You're correct, actually. I misread the original issue.