If you start the game, go into the Controls section of the options from the main menu, change the key for Toggle Equipment, Accept and quit the game, is it reset when you restart?
If you cleared the hotkey, rather than remapping it, try changing it to something else, that you wouldn't otherwise use, or hit accidentally (Ctrl-E, or something). Some 'missing' hotkeys for certain functions can be 'fixed' on startup if they are cleared.
