I've found some rather severe errors in the editor when I have MJ2 installed and have found it to be related to the inclusion of the MJ part modules in every command part.  Clicking/Copying a subsection of my craft, that has a command part on it, will cause a nullReferenceException, things slow down drastically, and I can't delete the grabbed part with the delete key, nor place it or drop it.  I have to either ctrl-z/undo or click on a new part in the inventory to cause it to delete. 

But this does not happen when I uninstall MJ2 or disable partless inclusion of MJ into all command parts by renaming MechJebNoCommandPods.cfg.  It only happens when the subsection of the craft copied/selected has a command part on it.  It also seems correlated to larger craft with many control parts, like a stack of satellites or similar. It does not happen when the same craft and subcraft sections have partless disabled and instead have the MJ AR202 part attached

Debian Linux 11, KSP 1.9.x-1.11.2, latest MJ2 from CKAN, quite a few mods. 64GB RAM, no swap in use

CORRECTION: After saving the craft and going back in to edit it again, I get the same problem all over again even with non-partless. Logs to follow