I noticed my AB not lighting off once. I did some reading and if I'm not mistaken, found it in the actual manual of the F-5 in the engine limitations section that going mil to max and back again can cause the AB not to fire and may even cause an engine flame out. Also, to avoid going from lower throttle settings to max at higher altitude and high G maneuvers. You should pause a moment at Mil before going Max.
Basically, I'm not convinced it's a bug. If anything, the engine behavior might be a little too lenient.