Please see the attached report for a reproduction of this behavior.

As you can see, the crosstab has only one row group in the group explorer which has its PageBreak property set to None. However, in the report explorer, you can see a greyed out row group I deleted with PageBreak=After which results in page breaks being inserted even though the group was supposedly deleted. In order to reproduce this, it appears that you have to first delete the column only and then delete the group, and you are left with a grey "ghost group" in the report explorer. If I delete both at once this does not seem to happen. I'm on version 15.0.21.120