I currently work inside a system that any new tools get created as an ASP.NET custom server-side control, rather than a Forms or MVC page. One of my most recent projects is to convert a Forms page into a control (basically moving from an old site to the current one), and as far as I can see, this requires very few changes. Most of the changes that make this "work" are in the header section (Change Page tag to Control tag, make a few tweaks behind the scenes, etc).
However, despite most of the pages I've converted into controls working perfectly, this one control does not want to refresh properly. It is supposed to refresh to show processing and completion when a button is hit, but it only updates properly about half the time. I've tried adjusting the UpdatePanel, the content template, and the relevant controls inside, but it keeps wanting to act flaky.
Ultimately, my question is, what is the difference between a full page and a control that would cause this shift in behavior, when I try to keep it as close to the (properly working) original, and the few minor tweaks I can see possibly helping, actually have no effect?