When you swap clothing out, in this case a shirt for another one, instead of dropping on the ground, the piece of clothing on your person disappears. This is a BIG bug, because everything inside of that piece of clothing also disappears. It doesn't teleport outside of the tent/garage/barrack, ect., it just disappears.
Clip: https://clips.twitch.tv/PlayfulTardyFishAMPEnergyCherry
This happens rarely, but many, many times.