Some win7-vintage touch drivers occasionally fail to send touch-end events. We suspect the failures happen when multiple touches happen at the same time (via mashing your hand and fingers into the screen.)

Although touch-end events don't fire, the drivers do accurately report the number of active touches. Thus our workaround watches for touches that disappear from the active touch list without sending a corresponding touch-end. When we detect that we generate a simulated touch-end.

There is an UMA stat (TouchScreen.MissedTOUCHEVENTF_UP) that tracks the number of times that the workaround fires. We should track that stat and watch for diminished usage - this would indicate that users are no longer using Win7, and that this workaround is no longer needed.

Note: In this bug, the term "driver" should map to the hardware driver + the OS support in Win7. It's unclear where in that stack the failure happens.

We've seen this in Dell Optiplex AIO 9020 and 7010 (touch versions) and Lenovo Horizon (tabletop)

See  issue 792892  and issue 316085 for more discussion.