Parenting Issues?

Alright, so a few days ago I found an updated advanced duplicator and decided to give Gmod 13 a whirl again after putting it aside awhile. Most of my old dupes work reasonably well with the new physics stuff that’s been implemented, so no problem there. I spent a few days building a submarine and without gcombat, I decided to put that on hold for the time being after finishing the frame. This is where my problem arises. Earlier today a friend and I were on a server hosted by myself doing work on some new aircraft. It seems that adding stuff to the old planes is perfectly OK, however replacing stuff or making an entirely new aircraft is problematic. The planes spazz and do not fly. We think it’s linked to parenting (we both tested planes with and without parenting), thus the reasoning behind this post.

Long story short: what has happened to parenting or Garry’s Mod to cause this problem, and how can it be fixed?