First of I should maybe explain that I'm currently making an add-on that enables the layer to build his own shp out of modules. As such everything about the vessels is dynamic, I can't know in advance what the player will actually build. This has nothing to do with the actual problem, but it prevents some potential solutions to the problem.
So, here's what's actually happening: I cannot transfer UMMUs to a vessel with multiple docking ports (every docking port automatically also becomes an airlock). Everything else works. I can transfer crew from a vessel with multiple docking ports to a vessel with only one docking port. I can transfer between vessels that both have only one docking port. I can correctly EVA and ingress a UMMU through any docking port of a vessel that has several. The only thing I seem unable to do is transfer a UMMU from a vessel to another vessel if the target vessel has several docking ports. This I write to show that there is nothing wrong with my airlock shapes per se. They all work very well.
Here's what happens: I dock two vessels, in one select a crewmember and the docking port which is docked to the other vessel. Then I transfer the crewmember.
The return code tells me that the transfer was succesful, and the crewmember vanishes from the vessel. However, the crewmember does not arrive at the other vessel. Instead, a mesh-less transfer UMMU is spawned at the currently active docking port of the other vessel, but it is never ingressed (nor can I ingress it manually, for that matter).
Even if I set the active airlock of the receiving vessel to the port the sending ship is docked to I get the same problem: The crewmember leaves the ship, but won't enter the other one, being condemned to a non-corporeal existance between the airlocks.
As I said, this only happens if the receiving vessel has multiple possible airlockpositions (i.e. is able to change the airlock shape), but even if the airlockshape is set to the docking port the other vessel is docked to.
Just to repeat, I can EVA a crewmember through the very same airlock and ingress it again, so there seems nothing wrong with the airlock shape itself.
Dan, do you have any Idea where my problem might lie?