Impossible to remap LMB or RMB to any action

[herasymenko-bohdan]

I have a fairly unusual control scheme, which does not use LMB and RMB as primary/alt fire, but it is impossible to remap those buttons to any other actions. In fact, even if the original mapping is "cleared", it cannot be assigned back. So the only way to reassign those buttons is by resetting everything to "default".
I wonder if it would be much trouble to fix this bug by allowing the LMB and RMB buttons to be assignable to any action