Changing the visible text of collapsed blocks

Hi,

I'm writing a Visual Studio Extension to customize my editor.

I would like to change the text that is displayed when a block of code is collapsed.

I tried "Walkthrough: Outlining" (http://msdn.microsoft.com/en-us/library/ee197665.aspx).

I works fine if I collapse blocks by clicking on the "+" sign, but the blocks don't collapse when I use Ctrl+M+O.

I guess the problem comes from the fact that I'm creating regions that already exist...

Could anyone tell me where to start?

Thanks.