I noticed this in a versus match today. My team was Nebula, Rocket+Groot, and Vulture, and on the enemy team, everyone was dead except for a second Vulture.
I fired off “One Fell Swoop” to make a green countdown and then went airborne. On the enemy’s turn, they fired a Jubilee “Light Show” team-up that changed my countdown purple. When my Vulture landed, the countdown was not removed and no damage was dealt to the enemy team.