You have to remember that to RMA the card, the shop will need to prove to the manufacturer that there is a fault. So they need to be able to reproduce it quite easily. If you can't see the error again after 3-days idle then it's really unlikely the shop will be able to either. Especially given that their software environment will likely be different to your own (unless you supply a VM I suppose.. though I don't think they're an accepted gaming environment yet - but even then ruling out a software error is quite an ask).
So, assume it's a software bug and either forget about it, or take the measures I suggested in my first reply to reduce software power state change issues.