If you change this line:

XComTacticalController(PC).m_XGPlayer.GetPlayableUnits(Units);

into:

XComTacticalController(PC).m_XGPlayer.getOriginalUnits(Units);


in your classfile "UISoldierQuickIconPanel.uc" it should work just fine

I recognized it when soldiers getting stunned or bleeding etc.,
if you sava the game and reloads, all charaters set to 0 moves including deadsoldiers are removed from the quickicon panel, this call above instead of the other one fixed it atleast for me. After recompiling, all squad members the mission started with will be shown in the panel no matter what.