Is mixology bugged?

So I have 2 chars with alchemy on Wotlk. One is pot master other is elixir master. Both have mixology and their alch specialization in spellbooks. One who's pot master has 430 alch skill. On this one strange behavior of consumables alch is observed.

When I drink elixir I have 2h duration of the buff. When I drink flask (forst wyrm) I have 1 hr. duration of it. Is it bugged or not?

it works on things you can create yourself, you need to learn flask recipes and you will have double duration+effect