Bannerman doesnt work, if you get a banner form another player

Hello

Me and a friend is playing together, im carry and he's semi support with banners.

We both have the Bannerman notable in the skilltree, he gets the linger effect
after he leaves his bannerarea, when i leave his bannerarea, i dont get the linger effect.

is it a bug or is it supposed to be your own banner area that you have to leave to get the effect?

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