This exact issue has been already discussed before with woritem [16321](https://ajaxcontroltoolkit.codeplex.com/workitem/16321). I was not able to find any other recent discussion about it.
I invite to read that report because symptoms are very well explained by the author.
I updated toolkit version from 30930 (Sep 2009) to 7.1213 (Dec 2013) on a project containing a complex implementation of TabContainer. Before the update I had no issue at all with that page and TabContainer in general, but as soon as I referenced new toolkit version I found out some strange behaviors.
I reduced it all in a very simple, standalone page, attached to this post.
Basically what happens is that when you set one or more tab to be invisible (no matter whether you do it by the attribute on tag declaration or in the code-behind), TabContainer starts to display mixed-content tabs after ActiveTabChanged event, when index requested is equals or greater than the one of the not visible.
Page attached shows it very clearly.
Note: none of the workarounds proposed in the old workitem is working in my environment.
Target framework 3.5, Toolkit version 7.1213, IIS 7.5, Windows 7 64 bit
Comments: Thanks to billhall555 for the information about October release: it could be useful if I can't fix with some workaround. In the meanwhile I ran other test and found out that the component is actually broken in more than one aspect. One above all: Tabs are not keeping their state after callback. You can easily verify that by going directly on the [online Tabs Sample](http://www.asp.net/AjaxLibrary/AjaxControlToolkitSampleSite/Tabs/Tabs.aspx) page. On that page, try this: * On the first TabContainer demo, uncheck 'Show Controls Owned' checkbox: 'Controls' tab will be greyed out as it becomes disabled * Change tab to 'Email' * Hit 'Save' button (it will cause a full postback, as demo itself informs): after that you will notice that 'Controls' tab becomes enabled again. This can be replicated on any TabContainer implementation: each time you need to disable (or hide) a tab you will run into that issue. Probably this should be submitted as a new issue, anyone who reads and feels confident to do so is welcome: I ran into this trying to figure out some workaround for my project and I didn't do enough test to cover the matter.
I invite to read that report because symptoms are very well explained by the author.
I updated toolkit version from 30930 (Sep 2009) to 7.1213 (Dec 2013) on a project containing a complex implementation of TabContainer. Before the update I had no issue at all with that page and TabContainer in general, but as soon as I referenced new toolkit version I found out some strange behaviors.
I reduced it all in a very simple, standalone page, attached to this post.
Basically what happens is that when you set one or more tab to be invisible (no matter whether you do it by the attribute on tag declaration or in the code-behind), TabContainer starts to display mixed-content tabs after ActiveTabChanged event, when index requested is equals or greater than the one of the not visible.
Page attached shows it very clearly.
Note: none of the workarounds proposed in the old workitem is working in my environment.
Target framework 3.5, Toolkit version 7.1213, IIS 7.5, Windows 7 64 bit
Comments: Thanks to billhall555 for the information about October release: it could be useful if I can't fix with some workaround. In the meanwhile I ran other test and found out that the component is actually broken in more than one aspect. One above all: Tabs are not keeping their state after callback. You can easily verify that by going directly on the [online Tabs Sample](http://www.asp.net/AjaxLibrary/AjaxControlToolkitSampleSite/Tabs/Tabs.aspx) page. On that page, try this: * On the first TabContainer demo, uncheck 'Show Controls Owned' checkbox: 'Controls' tab will be greyed out as it becomes disabled * Change tab to 'Email' * Hit 'Save' button (it will cause a full postback, as demo itself informs): after that you will notice that 'Controls' tab becomes enabled again. This can be replicated on any TabContainer implementation: each time you need to disable (or hide) a tab you will run into that issue. Probably this should be submitted as a new issue, anyone who reads and feels confident to do so is welcome: I ran into this trying to figure out some workaround for my project and I didn't do enough test to cover the matter.