Nested collapsible set into a collapsible set

Nested collapsible set into a collapsible set

Hi! JQM team! 
I first want to say that i had a lot of fun to use JQM framework! Thanks a lot! Usefull and easy to use! Very good work!
I'll be glad if my problem contributes to your community.
Here is my problem:

I got a collapsible set (main menu). This one contains nested collapsible set (sub menu).
When i expand an item of the main menu it works fine. Sub menus appears. 
But when i want to expand a sub menu item it close all menus items bringing us back to main menu items.

here is my code
  1. <div data-role="collapsible-set">
  2. <div data-role="collapsible">
  3.       <h3>main menu1</h3>
  4.       <div data-role="collapsible-set">
  5.                                   <div data-role="collapsible">
  6.                                          <h3>submenu1</h3>
  7.                                          <p>submenu1 content</p>
  8.                                  </div>
  9.                                <div data-role="collapsible">
  10.                                       <h3>submenu2</h3>
  11.                                       <p>submenu2 content</p>
  12.                                </div>
  13.                 </div>
  14. </div>
  15. <div data-role="collapsible">
  16. <h3>main menu2</h3>
  17. <p>content main menu2.</p>
  18. </div>
  19. </div>
something wrong?
Thanks for help!