As you can see here, when trying to press O to reach the iChun mods settings, the controls menu pops and O is typed in.

Doesn't happen with other letters as far as I could tell.
Any idea why this happens?
Thanks!

Firstly 1.7.10 isn't supported.
Secondly I have no idea what is going on in your gif with those custom animation, no idea where it starts or ends.

Ichuns way of accessing his keybind is incredibly stupid.

Custom animation is by the VoxelMenu mod. And as I said, it starts by trying to press O to reach the iChun mods settings, and ends by the controls menu popping up and O being typed in.
Thank you anyway!