After the latest IE 11 update the Layer List Widget expand arrow is no longer showing up. This only seems to be the case for API v3.16 and the latest IE 11 build 11.0.9600.18231 (Update versions 11.0.29). I believe this is the update that broke it https://support.microsoft.com/en-us/kb/3139929#bookmark-nonsecurityfix
This issue can be seen on the sample page with the correct IE 11 version
There is no issue in earlier versions of IE or any versions of Chrome that I can see. Also, if I revert back to API v3.15 the issue seems to disappear.