CSS calc(percent - pixels) being interpreted as calc(percent - percent) by browser

Okay, so this could be a really simple thing that I've done (one of those days) but I cannot for the life of me figure this one out.

Long story short, In my main.scss:

.test{
    width: calc(100% - 50px);
}

In my auto-complied main.css (viewed in code editor and even online file manager):

.test{
    width: calc(100% - 50px);
}

Yet, in the browser it isn't displaying correct and on inspection, it has somewhere been converted to:

.extra-test{
    width: calc(50%);
}

Any ideas on what could be causing this?

(Using latest version of Chrome)