Fairly easy to replicate.
1) You can be any class alien, if the commander on the marine team beacons, the dead body of that player also beacons back (I know its kind of obvious to see 4 dead guys go to no dead guys in a split second) Still should be looked into if possible.
2) Certain marine guns have certain hand postions for the 3rd person model (example the knife). While building only the weapon disappers, retaining the orginal hand position.
Thats all I can spot for now, if I notice anything else, Ill be sure to post it.