IE11 font size rendering rem/em calculation bug

Created by: thomaswelton

See: https://connect.microsoft.com/IE/feedback/details/816709/ie-11-calculating-font-sizes-wrong-when-setting-the-bodys-font-size-in-relative-units

Also in my testing of IE11... Bootstrap sets the font-size on the html element to 62.5% which should mean that the font-size is 10px. This is nice as in my own CSS I can easily calculate rem values for font sizes, widths, margins ect. However in IE11 the computed font-size when using a value like 3.9rem ends up being a pixel value of 38.74px instead of what is should be 39px

If I set the base html font size to be 10px instead of 62.5% rem calculations work as expected.