Basically:
Bind the open terminal keybind to Mouse 4 (if you have one) or Mouse 3, and it won't actually open the menu until you press any other key (moving will open it). It should just open when you press the mouse button.

Why these issues are died? 2023 is going and these still actual

Gonna necro this, but this issue doesn't seem to be AE2 specific, as the same happens with iron backpacks. It seems to be a 1.12-specific issue, or an issue with how the keybind is detected in general in 1.12.

My workaround was using my mouse's software (GHub) to bind my mouse key to a random useless keyboard key, then bind that one inside minecraft.

I can confirm this behavior as well. Using a regular keyboard keybind works as expected. Assigning the keybind to a mouse button does not open the AE2 terminal unless immediately followed up by another keypress (except for 'E') or movement.