Symptoms:

I have a WPF app that I'm testing on a Samsung XE700T1A tablet. I have no other tablets to test it on. Upon launching the app, when I rotate the tablet to portrait mode, my UI elements stop responding to touch. They continue to ignore touch after rotating back to landscape again, but then after rotating a third time back to portrait, touch works. Further rotations seem to have indeterminate results. Sometimes touch works, sometimes you have to keep rotating to get it back. I have seen an occasional variation in that initial sequence, but for the most part it appears very consistent.

In order to narrow down the range of possibilities, I created this simple WPF app to demonstrate the issue.

Solution:

This is apparently an issue known internally at Microsoft where "WPF's touch system does not always detect resolution changes correctly."

http://social.msdn.microsoft.com/Forums/en-US/wpf/thread/41e0bf65-2e96-4d0f-98aa-2c0cf31aa493

Paraphrasing comments there, the workaround is to subscribe to SystemEvents.DisplaySettingsChanged and after a short delay, repost WM_DISPLAYCHANGE to the "SystemResourceNotifyWindow" in the current thread.

However, the actual code posted there is not practical for anyone outside Microsoft. The code I've posted here will work for the rest of us.