R73 missile

Is this normal? I shot my r73 at a target abt 1.5km in a head on type situation, my r73 was pulling fine and was gonna hit, and it just went into a flat spin, yes a flat spin, it was still burning in the flat spin. And also today my missile missed a fully afterburning f14, it didnt even run out of speed, it just decided to miss (it pulled like 20gs and gave up)