Actually, you don't lose the rested exp, its Only if you play the account before renewing, mine also went inactive when the bank changed my CC number because my other was stolen, so it didn't get paid for 2 days. I did not lose any rested exp, I also didn't play it as a f2p account either. And yes, it went inactive/preferred after f2p launched.
Inactive means unused, not unsubed while you try the f2p model.