There's a few of these threads around, and this one seems most appropriate :p
I should have listened to advice on the forum, but did i? No, i lost 3 Armor pieces when i equipped my units with a new item, without de-equipping the old one first.
Out of the 4 units i equipped only the Horus mask came back to inventory, the other 3 disappeared. It's 1 Nisfit helmet, and the other 2 are ór Nisfit helmet ór Sissel shield. My strongest armor pieces, but i forgot if i had 1, 2 or 3 Nisfit's.
It's in my personal army, but i started training GA units before i switched gear, maybe that's relevant.
I hope you all had a good Halloween event, it was fun

(except the part where i forgot to start a big production at the end, grrrrrr)