So there shouldn't be too much going on in the page I'm having the issue with.
The cause of this issue was a recent upgrade to the latest (or close to) telerik dlls. Prior to that this issue was not occurring and no code has changed other than the telerik upgrade. We are using DotNetNuke as well.
Basically, there is an asp:panel that contains a few search filters, namely an id search textbox field. When the search button is clicked, the value of the textbox is read and the panel's Visible property is set to false and another panel's visibility is set to true (to show the results). The user may click a "return" button which does another post back that sets the initial panel's visibility back to true and the results panel back to false.
After this happens the RadTextBox that contains the id search will continually postback the previous search value even though the user had entered something else. The textbox is clearly posting the correct value when inspected with chrome's debugging tools (via network request capture you can view the form data).
To verify this is specific to RadTextBox, I replaced the control with a normal asp:TextBox with no other changes and it worked properly as expected.
Can I get some guidance as to what may be going wrong here? I've done hours of debugging and trying different things and have not figured out the cause.