multi-touch: Not getting secondary touch events if primary touchpoint is released or stationary

I'm developing a multi-touch app in Win7 using an HP tm2 (which supports 2 simultaneous touchpoints) and I'm seeing the following:

This sequence produces expected behavior:
-Start dragging finger 1: touchevents begin streaming.
-Start dragging finger 2: touchevents continue to stream, now with 2 touchpoints
-Release finger 2 while continuing to drag finger 1: touchevents stream with just the original touchpoint
-Release finger 1: touchevents stop.

But this does not:
-Start dragging finger 1: touchevents begin streaming.
-Start dragging finger 2: touchevents continue to stream, now with 2 touchpoints
-Release finger 1 while continuing to drag finger 2: all touchevents stop streaming. I get no touch releases when either finger is removed.

It seems that releasing the primary touchpoint prohibits updates from non-primary touches that are still in progress. This makes it hard to go from pan to pan+zoom by adding a second finger, then back to pan if the user releases the primary touch first.

I'm also seeing this in the Qt fingerpaint demo app... A quick test in the windows 7 Paint.exe has the secondary touch continuing to update as expected when the primary touch has been released or is stationary, which suggests that hardware and OS are functioning correctly.