Okay, so I've figured out the ins and outs of most of this, but I've found something that I thought might not have come up before. If you try to put a sign on a ship (whether physics for that ship are turned on or not), it gives an error about going past certain coordinates where "airships are stored," and disallows interaction with any ship at all. I seemed to be able to break non-ship blocks around me, though.
Attempting to exit and reload the world causes Minecraft to hang, and I had to kill the app and completely reload in order to reenter the world. So signs are probably bad for the same reasons beds are.
Two things: if you're using the 1.10.2 or 1.11.2 versions, those aren't supported and are extremely buggy. All users are advised to use the 1.12.2 beta builds (from http://jenkins.daporkchop.net/job/Valkyrien-Warfare-Revamped/), and won't get any support otherwise.
Also, I can't seem to reproduce that, so :/
I'll see if I can remind thebest to update the OP again