Mouse Button 4 in combination with a modifier key is detected as Mouse Button 5

If Mouse Button 4 is mapped to "Use Item/Place Block" the sneak-click functions do not work. The click appears to be ignored as it doesn't trigger the non-sneak function either.

I have not done exhaustive testing, but from what I can tell this only affects Mouse Button 4. Mouse Buttons 2 (of course), 3, and 5 work normally, as do keyboard keys.

Edit: updated Description and Summary to reflect better information

---

From MC-78394:
"Use Item" bound to NUMPAD0; When I sneak (using the RSHIFT key) I can't shoot a bow, open a chest, or place a block. Basically, anything that requires the "Use Item" function.