Just noticed this with the latest release, 15.1.4. I have a tabcontainer inside an updatepanel with updatemode = conditional. Some of the tabs trigger a modalpopupextender via code-behind also via child updatepanel. Initially, the modal popup and background display on top like they should, but after doing an update on the outer updatepanel, the modal popups and background css appear behind the tab container. z-index is -6000 for backgroundelement and -5999 for the modal popup when this happens. Used to work fine prior to release 15.1.4.
Comments: It seems that this is caused by the fix of the [27101](https://ajaxcontroltoolkit.codeplex.com/workitem/27101) issue. These changes are reverted now. Would you please check your project with the latest version of the source code of AJAX Control Toolkit?
Comments: It seems that this is caused by the fix of the [27101](https://ajaxcontroltoolkit.codeplex.com/workitem/27101) issue. These changes are reverted now. Would you please check your project with the latest version of the source code of AJAX Control Toolkit?