In a run last night (sorry, I didn't think to take a screenshot), I was in the middle of a run with 4 wood and 1 gold chest. I had an iOS message for something else and left the app. Upon returning, the battle resumed appropriately, but I soon managed to find another wood chest, giving me 5+1 by the 6th (I think) round. When I ultimately finished the stage, however, upon awarding the ending bonus chest (wood of course), the total didn't change to 6+1, but instead stayed at 5+1. I assume some error-trapping logic managed to maintain the limit of 6 chests at the end, too bad