I read similar issue with window as well.
As a general rule, any thing that pops up dynamically (menu, dropdown, auto complete) should have z-index set such a way that it can be seen above all other items currently in the display.
For example, I created menu in one Splitter Pane and showing the target in another Pane (you can question why would I need that - and there can be better way around) - but the menu was hidden within its own frame and did not show up. I have tried the same thing in ASP Rad Control and had got it working.
As a general rule, any thing that pops up dynamically (menu, dropdown, auto complete) should have z-index set such a way that it can be seen above all other items currently in the display.
For example, I created menu in one Splitter Pane and showing the target in another Pane (you can question why would I need that - and there can be better way around) - but the menu was hidden within its own frame and did not show up. I have tried the same thing in ASP Rad Control and had got it working.