Legends are broken in IE 11 on 4.4.0

[LeeDr]

New functionality in this release to have expand/collapse legend on charts doesn't work in IE 11.

You can click the little expand/collapse arrow and it switches direction but nothing pops out.
Affects both Discover and Visualize tabs.

In this image, it was clicked to expand, but it's not visible;

Same on Visualize. clicking the arrow changes direction but neither shows a legend;

[epixa]

If you comment out the following flex property, the issue goes away: https://github.com/elastic/kibana/blob/master/src/ui/public/vislib/styles/_legend.less#L41

Now, I'm looking into why that is.

[epixa]

It appears to have to do with flex-basis. If I leave flex-basis as the default (i.e. auto), the legend properly appears in IE11. However, vertical and horizontal scrollbars appear around the histogram in IE11 at that point whenever the legend is open, so the "fix" will need to be more than simply using the default flex-basis.