Well the only thing I can find to back it up is from one of the Sony devs in 2006 from this thread:
http://crucible.samanna.net/viewtopic.php?f=10&t=1832
Maddoc on 24 Feb 2006 14:05
Sunyn, that's definitely not the way it's supposed to work.
The potions have an effective caster level assigned to them that overrides the caster's actual level, which means that the benefit you're getting from said potion is always going to be exactly as it was as if the caster was level 'X', where 'X' is the level assigned to the potion.
That said, I've already forwarded this on to our QA team to verify and make sure that it's working the way I've just explained, and if it's not, it will be fixed.