I just spent approximately 4 hours wondering why a report I was creating kept inserting pagebreaks after a row group in a crosstab even though I had set GroupKeepTogether=False. I discovered that some old parent row group that I had since deleted was still visible (but greyed out) via the report explorer even though you couldn't see it in the group explorer. This deleted parent row group had its GroupKeepTogether set to True and it was still having an effect on the report layout even though I had deleted the group long since. Why is this happening? It's quite unintuitive and confusing that deleted groups don't seem to be truly deleted and can still have effects on the report.
follow up: Is there any way for me to "clean up" the groups in the report explorer view without having to recreate the entire crosstab from scratch? There does not seem to be an option to delete them. I had some trouble creating the desired layout so I ended up creating and deleting lots of groups so it looks like a total mess and apparently can also have unintended side effects.