Issue burndown chart confusion

I don't believe this is a bug, rather a mis-understanding on our part as to how the Issue Burndown charts work. You will notice in this project for version 9.1, there are a total of (68) issues, of which (1) is still unresolved. The *Default issue context burndown chart shows us the total number of issues in the Version... the *On the fly burndown only includes the (1) remaining issue that is left to be resolved. Why when we filter and hide all the resolved issues does the burndown only show us the one issue for the entire iteration (version), not the burndown of issues over time?

Please see attached screenshots for more information.