That would be very odd I'd that were the case.
That would break the entire concept of the key controlling the install type. Well at least it would for this specific scenario.
Any info that backs that up out of curiosity?
Yes, it's odd why they did it like this. No info, I just tested it and it worked, I was sure it would complain about the fact I did a clean install when it tries to activate but no. It was a laptop with a new SSD I just reveived, booted from TechNet disc, used key from upgrade assistant, made partitions and formatted. After installation was complete it was activated.