I have a RadPanelBar inside of a RadAjaxPanel. When an item is clicked on the RadPanelBar, I dynamically load a user control that uses a ModalPopupExtender. After a button is clicked on the user control and it causes a postback, everything works as intended and I can click another item on the RadPanelBar and everything works. When the user control is closed by the CancelControlID property of the ModalPopupExtender however, it doesn't cause a postback and the next time I click an item on the RadPanelBar, the RadAjaxLoadingPanel persists.
What the page looks like on load before any clicks: http://i.imgur.com/drnCcNO.png
What the rad panel bar looks after click on an item: http://i.imgur.com/czikveQ.png
Modal Control is loaded: http://i.imgur.com/rDT07Yw.png
After Modal control is closed without causing a postback, when clicking on an item in RadPanelBar again, it seems to be even more dim: http://imgur.com/YZNmRpM
Now when user control is loaded again, the loading panel persists: http://i.imgur.com/TAXnRH4.png