System.Web.Optimization StyleBundler removes space from infront of + but not - when compiling and minifying less

Question

When using plain CSS calc in less I have to put a tilde before my calc string to stop less from calculating it, which works when doing - but does not when using +

What causes this and can I stop it from happening?

Examples:

width: calc(~"(100%) - 20px");

Results In:

width: calc((100%) - 20px);

But:

width: calc(~"(100%) + 20px");

Results In:

width: calc((100%)+ 20px);

Which is not valid css.

The only workaround I have figured out is:

width: calc(~"(100%) - -20px");

Results In:

width: calc((100%) - -20px);

Which is mathematically correct to do a + but why do the Bundling and Minification force me to have to do this?

As a side note, I use visual studio 2017 community and its bundling from the bundleConfig.cs

My style bundle looks like so:

    public static void RegisterBundles(BundleCollection bundles)
    {
        bundles.Add(new StyleBundle("~/Content/css/BundledCSS")
            .Include("~/Content/css/UpToDate/jquery-ui.css")
            .Include("~/Content/less/bootstrap/bootstrap.css")
            .Include("~/Content/css/font-awesome.css")
            .Include("~/Content/css/awesome-bootstrap-checkbox.css")
            .Include("~/Content/css/animate.css")
            .Include("~/Content/css/SidewaysNav.css")
            .Include("~/Content/css/site.css")
            .Include("~/Content/css/pastel-colors.css")
        );

        BundleTable.EnableOptimizations = true;
        bundles.FileSetOrderList.Clear();
    }