How to use AJAX NumericUpDownExtender inside AJAX TabContainer

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ASP.NET

I am trying to add a NumericUpDownExtender with a TextBox inside of an AJAX Tab Container. When putting just a TextBox on the form and adding the NumericUpDownExtender, the up/down arrows work fine to change the value shown in the text box.

However, as soon as I add a Tab Container and a Tab Panel, adding the TextBox inside the panel with a NumericUpDownExtender no longer works. Clicking on the up/down arrows has no effect in changing the value shown in the text box. When clicking on an arrow, it no longer shows it being depressed as if it is not even being processed.

I am, of course, adding a AJAX ScriptManager, which is needed to use the AJAX Controls.

How do I get the TextBox with a NumericUpDownExtender to respond when placed on a Tab Panel inside of a Tab Container?