I've got a fun one for you!
I've got a treeview that renders fine when placed inside , but when I place it inside (a control that derives directly from UpdatePanel) it shows the tree content, but doesn't respond to javascript events (like mouse hover or click).
CustomUpdatePanel can be a control with no code, i.e. it doesn't change the behaviour of the UpdatePanel at all, and it still fails to work properly.
If a wrap the tree like so:
Then it works again.
From the behaviour, I'm guessing there's some code that says something like:
if (AncestorControl.GetType() == typeof(UpdatePanel))
Instead of:
if (AncestorControl is UpdatePanel)
Just a guess though!
I just found the ForceAjaxRenderer property, and I'm guessing that will fix my problem.