Moin moin =)
Sorry, but why you don't understand it? ^^ Even with my very bad English I understand this =D ( maybe you just didn't play Vamprisim )
I don't know if you can change this, I saw it at so many maps and for now I don't know, how you can change something like that - sorry.
The problem: ( for you Raven0 )
You got 2 teams. Now if team 1 kills the builder from one player of team 2, this player becomes a member of team 1. While this player was in team 2, he can see this allies. When this player changed now to team 1, he still see the places on the minimap, where his ex allies build there bases - and that's the problem ( He want "clean" the minimap, so it looks like the same when the game starts )
Greetings and Peace
Dr. Boom