You must be using IE 8 or IE 9 in 8 compatibility mode. The approach in today's bootstrap responsive design caters to mobile devices "first" and then will attempt to scale upwards to support larger desktop screens. The minor downside is that older legacy browser versions such as IE 8 and below don't properly support media queries used in responsive designs for scaling all elements.
Since so many people these days are using mobile devices, responsive designs have become more relevant and often a key factor for many sites. However, responsive designs typically only support more modern browser versions, developers can only go so far in their attempts to create hacks to fully support older legacy browsers.
It has been tested and works fine in IE versions 9, 10 and 11 (exception: not version 9 if 8 compatibility mode is being used).