Extensions window not refreshing when programatically changed

I have a few extensions (3 and growing) that implement IExtensionConfig. The extensions are for doing different sorts of task in ArcMap, so they rely on different data loaded, enable different custom tools etc. I only want one extension enable at the time. So I added logic in IExtensionConfig.state set to check the state of the other extension when a user turns the extension on and display a message an disable the extension. That is fine but the extension window is not refreshed. If I close and reopen it, it appears correctly.

This is similar to this thread but it is not add-ins and that thread didn't have an answer.
http://forums.arcgis.com/threads/520...xtensionConfig

How to I get the window to refresh?