I'd say even simpler would be that the Imperials removed the vest from him, being sure to strip him of potential concealment spots for a weapon they missed. He is missing it when they drag him to Vader afterall and hand over the only weapon he had... Good pics from Grammie to support that he wore the vest on Endor though... I knew there were images somewhere that pertained to that.
The Endor Soldiers are my favorites of the wave as well CHEWIE, and I'll easily stock up on these like I buy Clones or Stormtroopers. I figure 20 of each at least, and I'll supply heads for them then.
I love the Falcon Gunner... The scenes in which they were used got cut, and you only see the additional command crewers in them. It is, for me, the uniform of the Commandoes that they wear for ship or street combat... They have different duds for different environments though.
For the curious, the outfit's actually inaccurate too. The pants should be pocketless. They actually wear a single-piece jumpsuit under the Commando vest, not the baggy pocketed pants and the undershirt thing.