The reset button for individual controls is reversed. The reset is clickable when the control is already set to default (effectively doing nothing) and is disabled when the control has been set to a user preference.
Issue is not present in vanilla Minecraft.
Environments tested:
14.21.1.2443 with installed mods
14.21.1.2443 without installed mods
14.21.1.2387 with installed mods
1.12
1.12.1