When you kill the enemy who is holding your flag, the flag goes to your base and back to where it should be (at enemy's dead body). We were able to reproduce it, I'm not sure when exactly it happens, if it depends on the distance between the flag carrier and your base, or if only one flag can be in possession at the time, or if you have to be the last man standing. Happened also on airtime, but flag flew through the walls (it just goes in straight line, same thing as if you sent it back and it came back right after that).
Tested on Arctic Public (62.108.40.110:22221), gameversion 1.922 (178), using new physics.
Watch the demo carefully, it happens right when the flag carrier is shot.