It is possible to add another key to existing binding but not possible to delete and unbind any key using "backspace" or "del" keys.

As mentioned in the bugs report forums its currently not working to let you remove bindings via options. However, you can always /bind <key> NONE to delete a binding, where <key> is the item you want to delete, for instnace, F12, j, J, or JOY-BUTTON-1. Keys are case sensitive, so shift-J and j are two different things.

tkyvm!

shouldn't this sort of thing be fixed immediately
its embarrassing that a paid for product cant even get the basics right

Actually, it did work once. It was broken due to an orthogonal change some time ago.

Yes, it's on a priority list, but keeps getting bounced around by other issues. We'll look into it.

well if this is on a priority list there's not much chance for anything that isn't