FL100C: one dataset, two charts, only one chart will display

I've written a custom dataset SQL query that produces me a count of how much traffic (GB) goes In/Out through our Internet link (port 16 on our FG200B) per day.  It works great.

Then I created two Charts based off this Dataset:  one is a Table format (lists the data values tabular format); the other is a Bar Graph.

Then I created a Report utilising the Charts ... and here is where it has gone pear-shaped:

If I embed the tabular data Chart by itself into the Report, it works.

If I embed the bar graph Chart by itself into the Report, it works.

If I embed BOTH of the charts into the Report, only ONE of them is displayed; the other has "No data".

I had expected that if I created a Dataset, then multiple Charts from that dataset, the FL100C would be smart enough to run the SQL query once, then reuse the results multiple times to drive the charts ... but it seems I am mistaken.

I don't really want to needlessly duplicate datasets, just so I can use that data multiple times in a report.

Suggestions welcome.