Warning: I'm no ASP.NET expert... If this turns out to be garbage, I'll delete it :)
A) I believe you will see the new values of all the controls, whenever the postback ends up happening, including all the change events, just as you described. The values have changed, after all - the AutoPostBack
just affects the timing (and whether the postback occurs at all, of course).
B) There's more Javascript in the HTML delivered with AutoPostBack = True
on all the controls, but not enough to make that enormous difference. As noted in your edit, it looks like that was a transient issue anyway - we can't really explain transient issues without more diagnostics.