try doing what i do when my hotkeys mysteriously dissapear/change on live servers.
there is some eky combination to change the assigned hotbar set on slot 1 (the main hotbar). iirc, hold down shift and press either f1 or just 1 for the first, f2 or 2 for the next, etc. i'm saying "f1 or 1" because i do not remember which it is, it's not both. try that out, if it doesn't work, try all of the change keys (ctrl, shift, alt) with f1-f12 until you find the right combination.
i'd try it myself, but i'm at work atm.