Confirmed Mystical Dispute / Cost Reduction Spells and F8(Auto-Yield)

[MickeyPlaysMagic]

If you have F8 (no possible play auto-yield) active and a mystical dispute or other spell that has its cost reduced in hand, priority will be passed unless you have the full amount of mana to cast the card. In this example, you need 3 open mana to cast dispute, but if you have 1 blue mana to counter another spell, F8 will pass priority without you having an opportunity to respond.

 

[Dilettante]

have had this happen several times

 

[TimelessPPZ]

If all lands are tapped,an there are no other spells can be cast. Disabling Bluff will stop give you priority to cast some cards that have a less cost，such as ‘out of air’ ‘mystical dispute’ and 'knockout blow'.Any player that tapping first to cost a spell can be lead to a unexpected yield.