I don't think that's true..
If it is, I honestly see no reason why they'd be kicked out.I don't think the man's intent of proposing is to steal anyone's shine.that's the last thing on his mind.
I guess he just felt the ambience of the wedding venue is just about right to propose to the love of his life.
Why, just the other day I saw this movie " the big wedding" staring robin Williams and Robert de niro.the father of the groom proposed to his woman right at the wedding venue.
I think its the most sweetest thing ever,and no one should be thrown out for that.