Just ran the same set of tests with the T-80U[M] with Refleks missile against M48A5. Same results, they will not engage with missiles even if the missile is the only available ammunition. If the munition type for the Refleks is switched to HEAT they engage as soon as the M48s are in range.

I also ...

I wasn't able to get the M60A2 to launch it's missiles at targets. I've run a number of test scenarios including with the loadout altered to include no HEAT rounds for the main gun and the tanks still refuse to fire missiles at enemy tanks. Enemy tanks were T-55A for the test scenarios. After those ...