Dropdown menu scrollbar broken in IE11/Edge

- What MDL Version are you using? (please be specific, e.g. _major.minor.patch_)
1.2.1
- What browser(s) is this bug affecting (including version)?
IE11 and Edge
- What OS (and version) are you using?
Windows 10
- What are the steps to reproduce the bug? Can you create a plunker/codepen/jsfiddle which reproduces it?
- Visit https://codepen.io/phanboy4/pen/kkqQvB in IE11 or Edge
- Note that there is no scrollbar in the dropdown menu
- Visit same codepen with Chrome or Firefox
- Note that there is a scrollbar.
- What is the expected behavior?
A scrollbar should appear in IE11/Edge as well as Firefox/Chrome.
- What is the actual behavior?
No scrollbar appears in IE11/Edge.
- Any other information you believe would be useful?
Changing `overflow-y` to `overflow` does introduce a scrollbar in IE/Edge, but it behaves oddly and an unwanted horizontal scrollbar is also introduced. This change does not affect Chrome/FF rendering.

Either I'm doing this wrong, or this is a browser bug that cannot be worked around and/or this is an MDL bug.