[Fern]

I've learned that this only seems to happen if you're doing Turnover while in Reaver Stance with Martial Lawbreaker.
So even if the weapon you're using is a Spear, so long as you're in Reaver Stance with Martial Lawbreaker, Excel Turnover won't occur.

Tested like this:
Turnover with LV3 Weapon Charge, no Reaver Stance = Excel Turnover happened
Turnover with LV3 Weapon Charge, Reaver Stance = Excel Turnover happened
Turnover with LV3 Weapon Charge, Reaver Stance AND Martial Lawbreaker on = No Excel Turnover
Weapon was Excel Hasta.