I reproduced the issue on my Surface Pro 2 running Windows 8.1, both with the touchpad and with the touchscreen. When doing the touch screen pinch zoom there are no updates while touching the screen, but upon lifting my fingers the page updates. When using the touchpad there are no updates until you do some other interaction with the page to cause repainting. So the issue also affects touchscreens as well as touchpads (which was a question up until this point).
Bug 1632443 Comment 15 Edit History
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I reproduced the issue on my Surface Pro 2 running Windows 8.1, both with the touchpad and with the touchscreen. When doing the touch screen pinch zoom there are no updates while touching the screen, but upon lifting my fingers the page updates. When using the touchpad there are no updates until you do some other interaction with the page to cause repainting. And the touchscreen issue doesn't need the direct manipulation enabled (which is expected). So the issue also affects touchscreens as well as touchpads (which was a question up until this point).