Aug 02, 2017 02:03 PM|mschelstrate|LINK
I believe that the issue may be with the dynamically created controls on the complex web page, one of which contains the popup window.
For some reason, the textbox and hidden fields retain their values in the code behind, but the listbox does not during the postback.
Rather than continue to troubleshoot this issue, I came up with a workaround.
I am then able to read the values in the hidden field in the code behind during the OnClick event, and use them to complete the required task.
Thank you very much for your continued support on this difficult issue.