Indicator is starting / stopping in IE vs smoothly changing

[Firestorm980]

Describe the bug
The indicator only updates on scroll end for IE versus continuously like other browsers.

Expected behavior
Indicator smoothly updates as the user scrolls.

[Firestorm980]

Here is a clip of the bug in action when compared with a span. It looks like it may actually be related to some inherent properties of using progress in IE. Notice how even though both elements update at the same time with the correct percentage, the progress bar takes a second to catch up, where the span is instant.

baseline-ie11-reading-position-bug.mov