As a temporary fix, you can add the following line to your "DCS World OpenBeta\Mods\aircraft\AJS37\Input\joystick\default.lua":
{down = 3006, up = 3005, cockpit_device_id = devices.NAVIGATIONPANEL, value_down = 1.0, value_up = 1.0, name = "T1 Fix (Hold)", category = "Radar"},
and then map the new command "T1 Fix (Hold)". I've used this for the first detent of my Warthog Trigger and it works fine there.