Got banner with 3 +1s?

Platform, device version and operating system:
Android, Pixel 4a

Screenshot or image:

What you were expecting to happen, and what actually happened:
Was fighting a dungeon battle, and I notice that the gear icon says I have +1 blue, +1 yellow, AND +1 brown, which isn’t any banner I’ve seen.

I don’t think I ever set the banner for this team, so maybe the default banner is better than any of the ones you can select? If so, I want to set that banner on my other teams!

How often does this happen? When did it begin happening?
I’ve seen this a few times, pretty sure always with teams that I haven’t set a banner for.

Steps to make it happen again
Choose new team which has never set a banner, go into battle, click gear on upper left.

You can get bonus mana from things other than banners. For example, Leprechaun adds +1 to green. Most likely you were using a class with the Stone Mastery talent enabled - Titan, Monk, Elementalist etc