modal region not opening after page submit

OK, here's my situation. I have modal region with a chart. There are checkboxes corresponding to each line on the chart. I want the end user to be able to click a checkbox and have the corresponding line on the chart appear/disappear. Here's where I am:

1. User opens page two
2. There is a button "open chart" at the top of the page
3. When that is pressed, chart opens
4. User hits a checkbox, the page is submitted with a dynamic action
5. The modal region disappears
6. When I open the modal region back up, the line has indeed disappeared like it was supposed to.

My problem is number 5 above. I need that modal region to stay open after the dynamic action on the checkbox submits the page.

So far, I have tried another action (under the submit page on checkbox change action) that opens the modal region. But, that isn't working. Any help is greatly appreciated.