A rescent patch made it so that fighters no longer contribute suplies to a fleet. Looks like they don't share amongst themeselves either.
__________________
I do not know with what weapons World War III will be fought, but I know that World War IV will be fought with sticks and stones.
-Albert Einstein
Ok, I confirmed that the fighter resupply bug is inherent to unmodded SE4 Gold at least in v1.84. A fighter stack will not be resupplied at a Resupply Depot if the RD is on a moon. They get resupplied fine if the RD is not on a moon.
I emailed MM about this bug and the fleet supply bugs.