How To Draw

I have a unique problem in Dota 2... when I open the shop menu (the little side bar) or when I level up and need to upgrade an ability, there is this MASSIVE FPS drop.

I have no idea of what is causing that and otherwise the game run mostly fine. Any suggestion?

I'm halfway thru Axiom Verge, but I'm can't say much because SPOILERS. Suffice to say I recommend it specially if you like Metroid and remember, Athetos is kill.