Less not compile viewport units (vmax)

Question

I use ASP.NET MVC 5 with LESS (bundle & dotless and LessTransform package). But less incorrectly compiles css viewport unit "vmax".

width: 20vmax;

and get output (vmax with space)

width: 20vm ax;

others viewport units (vh, vw, vmin) compiles correctly.

How to fix this error? Thanks

UPD 28/08/2015 I solved the problem as follows:

I removed less bundle

var lessBundle = new Bundle("~/bundles/less").Include("~/assets/css/responsive.less");
lessBundle.Transforms.Add(new LessTransform());
lessBundle.Transforms.Add(new CssMinify());
bundles.Add(lessBundle);

and create new default styleBundle. I link compiled .css file, but not .less

bundles.Add(new StyleBundle("~/bundles/app").Include(
                    "~/assets/css/responsive.css"));

and it works