I scroll with two fingers on my mouse pad, because I want to the end of the document. I don't touch the mouse pad anymore. The document is now sliding. In the time it is sliding I want to press Ctrl and then zoom with + and - to a proper size. (In this time I'm simultaneously analyzing the pages to find the spot I want to look at.) But then the document is zooming almost to infinity with the rest of the momentum from sliding.

Now a reason why it is not an feature:
When the cpu is busy and there is not much time to render the sliding properly one could think the document already stopped sliding and the momentum is gone, but in reality it is not. The next rendered frame is now a white screen, because the view is somewhere lost between two letters.
This 

Reproducible: Always

Steps to Reproduce:
1.scroll with mouse pad, very quickly on a large file. Give it much momentum.
2. press Ctrl

Actual Results:  
The document gets lost in zooming

Expected Results:  
let the document sliding. The performing of the command to scroll is over. Now the Ctrl should not interact with last command anymore.