It's just the way it is, and not a bug. It comes down to how much texture space on the sheet is devoted to each section of the model. In this case it seems the artist put a higher value on ensuring the bandolier remained detailed while sacrificing texture space on the remaining chest piece (probably because it's mostly hidden underneath the bandolier). It's just a judgement call.
It may also be that the chest piece is made up of several texture sheets, and (again) the bandolier got the lion's share of the resources.
