Hi,

When using the recipe/uses keys as r/u, everything works fine, however when I rebind these to Button 4/5 (Buttons on side of mouse), the recipe/uses only works on the JEI display, and not on items that are physically in an inventory (e.g. my inventory or a chest).

This issue was not occurring in any 1.12 modpacks, and occurs in all 1.16 modpacks I've played (Valhelsia3 , DW20 1.16, and a custom pack).

Forge Versions Tested: 36.2.22, 36.2.24, 36.2.26
JEI Versions Tested: 7.7.1.139, 7.7.1.145

I have tested this with only Forge and JEI installed, no other mods and it still occurs.

I have also been having this problem, in Enigmatica 6. I did discover that if I use my mouse software to rebind a side button to 'u', it works as expected. Trying to bind the button directly, as per the OP, doesn't work.

Thanks for the report! This has been fixed in the latest version 9.4.1.99, which should be available shortly.
I'll work on backporting this to 1.16.

Please note that you will still not be able to use left-click, right-click, or middle-click because these keys conflict with the vanilla gui's normal behavior. Other buttons should work now.