Editing in IE 11 breaks at resolutions below 1400px

[Cheddam]

Affected versions: SilverStripe 4.2 and later (testing incomplete, screenshots are from 4.4-RC1)

When loading a Page in the Edit Mode view in IE 11, at resolutions below 1400px wide, the resulting UI will be this:

Resizing the window in either direction fixes this issue, although at widths 750px or less, the UI is permanently broken:

The resizing fix doesn't always work, and the UI breaks again when opening a different page for editing. This appears to affect all pagetypes (Elemental-powered or not).

There are a couple of existing issues related to editing pages in IE 11 (#2245 and #2345), and I'd summarise the current state of editing in IE 11 (on displays below 1440px wide) as "unsupported".

[robbieaverill]

I’ve triaged this as critical because IE11 is a supported browser, and this makes it unusable. Happy for someone to argue otherwise and reduce it though.

[brynwhyman]

We'll look at this after looking to resolve #2245

[NightJar]

During testing I'm able to "restore order" by clicking the "show the site tree" button

[Cheddam]

This issue has been resolved, and the related fixes are available in SilverStripe 4.4.3.