I use tab key for my game input scheme (holding it, specifically). In studio after like 0.5 secs of holding it, it starts selecting/browsing through elements of the studio UI.
I dont think tab should have this behavior in play mode, at least not while focused in the game window.
Alternatively, tab should do nothing unless you have selected some UI element already (and if it already works like that, then no UI element should be selected by default when a new studio window is opened)