How do I stop this from happening?

[PoorOldSpike]

Infantry won't fire small-arms against buttoned tanks

This time I buttoned the T-34 before setting it rolling.
I left the infantry on 'free-fire' (no arc, no hide), and the first squad threw a grenade (ringed) when the tank got near, scoring a Hit (inset), he and the other squads never sprayed it with small arms because it was buttoned.
For the record the Hit did no damage and the tank kept rolling, still buttoned, with all the squads watching it but not firing SA.
One more grenade was thrown later in the turn by another squad (miss) making a total of 2 thrown during the turn.
The tank never spotted any squads because it was buttoned.
Interestingly, the tank auto-unbuttoned in the last few seconds of the turn and the squads immediately began small-arming him and he quickly buttoned back up, confirming that if infantry get a clear shot at an unbuttoned TC they'll take it (unless on 15m arcs and Hide)
Tactical note- the test shows you want enemy tanks to approach your inf buttoned so they'll hurl grenades at it rather than spray it, so it might be a good idea to order a squad or MG/ light mortar etc (behind the front line somewhere) to fire at tanks to force them to button before they get close to your front line grenade-throwers.