When you make a trade it wipes everything from your inventory from Volt oil down. It can also double up the mats like so, http://steamcommunity.com/profiles/76561198009308385/screenshot/54177888...

I'm sure you guys are aware of the problem but please issue a statement whether or not it is safe to trade via steam!

Also more info here http://forums.steampowered.com/forums/showthread.php?t=2103255