I think the I_TGT system is modeled from an auto-pilot script (possibly). When I open it it accelerates & decreases speed in a glitch. I tent to open it up as I taxi - about 4km per hr should do it. The flight comes to a complete stop and allows me to pre-plan an attack.

If I open the I-TGT in flight it decreases my speed to 0km immediately ! it then recovers. It's just something I live with, the modeler has done a great job, however until there is a vanilla GPS/weapon system implemented in Arma we just have to live with it. Personally for me I would make such a system a priority.