If I lock a drawer with items in it, then unlock it and take out the items, I can't put any other items in it except that one type. There seems to be no way to clear the saved item which has a quantity of 0. How can I do this?

Incidentally this has been bugging me for a few weeks and I have a fix queued for 1.14+. You haven't specified which version you're playing on though.

Workaround: place same item back in, unlock drawer, remove item.

Fixed in latest 1.14 and 1.15

Is there a chance this can also be fixed for the 1.12.2 version, or is that no longer supported?