If you have a window.showModalDialog called by your .Net application, you might have the problem that the Page_Load event only fires one time.
After doing my research, I found out that if the Page_Load event doesn't fire probably the page is being loaded using the cache and no roundtrips occurred.
To fix this, you need to add a unique query string in your URL of the window.showModalDialog to make the browser not to load in the cache.
Sample code with the unique query string:
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