WWGT questions:
Did you place the cWebList inside a cWebPanel or directly in the cWebView?
Yes

Are all your rows exactly the same height?
Yes but between each row there is a lil space created by CSS, might that result in the same issue?

Scrollbar is not broken.
If so, on what device? Doesn't matter, the issue is on every device / PC.
What browser? Doesn't matter, tested it on IE, Firefox and Chrome, all the same.

Can you provide a full sample?
See attached image. It shows the element explorer with a row selected and a screenshot of the grid that shows which row is lighting up (it falls outside of the grid).

So you are saying that the scrollbar is broken?
No the scrollbar is not broken, it works after a certain amount of rows. It will basically have invisible rows outside of the grid , but after a certain number the scrollbar will appear to scroll through, just the invisible rows will remain unreachable.
Click image for larger version. 

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