How do I re-enable input after dragging off iPad screen?

Touch input appears to stop detecting touches after dragging finger off screen onto ipad frame, then returning to screen. Is there a way to address this?

Repro:

1. add Debug.Log(Input.touchCount); to an update somewhere

2. tap, drag finger around ipad screen

3. "1" is output as expected

4. now without lifting, drag finger off screen, onto ipad frame and leave finger at that location

5. "0" is correctly output

6. without lifting finger off device, drag finger back onto the touch screen again.

Issue:

"0" continues to be output, even though I'm clearly touching the touchpad. This is the problem I'm trying to solve. Happens with ipad3/4

To restart the correct input logging I have to lift finger off screen, and back on again.

Has anyone experienced/fixed this issue? or is able to suggest a possible fix/workaround?

many thanks