New "swap items with offhand" feature doesn't work if the control is bound to the 4th or 5th mouse button

New feature released in Java 1.16 Pre-release 3 which allows to swap items with offhand directly from inventory (and swap don't work only if I swapping items from inventory, if try to swap items from hotbar, everything is alright) don't work if action "Swap item with offhand" is binded to 5th or 4th mouse buttons. Also, if reassign action to another keyboard key, everything is fine.
What is also interesting - in controls menu this buttons shows as "key.mouse.5" and "key.mouse.4", and this is issue of 1.16 (starting at 20w17a, actually), in 1.15.2 (and 20w16a) everything shows correctly.