I have created a custom cell type that derives from the 'GridDropDownCellModel'. On drop down, I am displaying a user control that, among other things, has a combo box. When I use the .NET combo box and attempt to click on it, the whole popup disappears. I swapped out the combo box with your ComboBoxExt control (which I would prefer to use) and get similar issues. I know it has something to with only having one popup shown at a time, but all attempts to manipulate popup parents and so forth have been unsuccessful. Can you provide some direction?