We have a page with a simple registration form with two asp:DropDownList controls and a asp:Button control. DropDownList1 fires the OnSelectedIndexChanged event to populate DropDownList2 (hardcoded, not from a database). When clicking the button, the OnClick event takes you to the next step (using the values from DropDownList1 and DropDownList2). The page uses a MasterPage.

This has been working fine all the way up to CMS 7.1.

After upgrading to 7.5+ (upgrade 12 is installed), somewhere along the line the form events stopped working properly. Only the value from DropDownList1 persists to the next step and the OnSelectedIndexChanged event for DropDownList1 incorrectly fires when clicking the button, thus clearing DropDownList2.

I'm not sure exactly at which point this stopped working but when testing the 7.1 version of the site everything works as before.

I have created a new non-EPiServer site with a test page and removed everything possible in the code except the dropdowns and the button. This works with a MasterPage. If I do the same in the EPiServer site it doesn't work when using a MasterPage (all functionality removed, just a bare MasterPage).

So, somehow when using a MasterPage the events for the controls on the child page do not work as they should after upgrading to 7.5+....

I've tested a number of things but are running out of ideas. If you have run into this problem or similar, any help would be greatly appreciated! Thanks!