The attached sample has a simple table with two row groups, and "header" rows created via "Insert Row -> Outside Group - above".
The groups have "keep together" set.

But despite this, the header rows render at the bottom of one page, with data rows on the following page. This should never happen, I can't think of any case it would be expected (it would be like having "Chapter 2" at the bottom of a page when the text for it starts on the next page). 

I also have a sample with just 1 row group, but with 2 detail rows, and the same thing happens. It only appears to work when there's just 1 row group and 1 detail row.