Yeah, we're aware of it. This is also what phzi was talking about a couple of posts back. The issue is with the stratum protocol, which currently doesn't support changing the extranonce1. Therefore currently the only option is to disconnect a rig in reconnect it to new order. We'll see if we'll find a technical solution for this.
It's possible to fix =). Multi-pools have had this issue in the past.
Hmm, stratum protocol actually doesn't support changing extranonce1 without disconnect, so I'd be very glad if you know how multi-pools solved this. And than again, NiceHash doesn't operate as a multi-pool behind the scenes, it's a quite different approach. But if you have some hint or a link please post it.