Versions < 1.3 have unlimited demo mode like Premium users

I was bored and just tried to test Demo.
I've created a new profile, logged out of my Premium account and logged to an account within Premium. Then I've selected it to run Minecraft 1.2.5 - and noticed, that when launching versions before 1.3 (When the Demo was introduced) you can play it like Premium user. No singleplayer limitations, multiplayer (however probably you can join only servers with offline mode (not checked)), etc.
I think that it should be changed so you can't launch versions before 1.3 within Premium.