No, I've never encountered that.

But I'm also not sure what qualifies as a bug here, given Microsoft's weird billing model. If you get charged for subagents, you'll burn through your premium requests in no time. If you don't get charged for subagents, you can get nearly unlimited usage of premium mode by using a go-between agent with a cheap/free model.

Currently I'm doing the latter, although I have to assume Microsoft will crack down on it at some point.