For the most part, SE officially supports the last two versions of browsers. IE11's a bit of an evolutionary dead end, with even its successor's engine moving over to Blink.
While it gets security updates, in essence it's a 6-year-old browser, primarily kept in modern PCs for the odd legacy site.
Currently official SE policy — as per the supported browser post says
This browser is mostly supported on a "because it works" basis. Support may be dropped in the future, without notice, if new functionality is implemented that cannot be made to work in Internet Explorer 11.
Now, this doesn't explicitly say any minor bugs won't be fixed, but "because it works" is pretty much the same level of usability one gets off a less common browser.
There's a laundry list of thing that is known to be broken on IE anyway - PNG, SVG and even JS works... differently.
So rather than leaving it on the supported OS list, it seems like a good idea to drop IE11 support formally. A good chunk of bugs feel like 'minor' rendering bugs in any case, so it wouldn't really hurt that much.