Hi,
I have reconfigured my keys because I like changing weapons with Q (as in valve-style games). Q was the default key for HUD lock/unlock so that option remained without any key assigned.
There is a problem with the hud in this case: if you lock it by clicking the small icon that should togle hud lock/unlock, you cannot unlock it unless you assign a new key and press that key.
So put it on a new button? Maybe 'H'?