You can't reproduce it because the example you have is different from the problem that I stated.
I have a flat datasource that is grouped by one column. I DO NOT have aa parent child relationship. Just a flat table that is group by one field.
I have a summary row at the top using a custom engine.
When I click the LAST plus/minus button, the summary in my CaptionSummaryCell disappears. They re-appear when I expand the group by clicking on the plus/minus arrow.
I have attached a (before and after) screen shot of this issue
ScreenShot34.zip