Breakpoint issue with flex-sm #5995

I want to apply a 100% flex on a child of a layout-row container only for small devices, but it doesn't seem to work since rc5 and it seems to be because of this code from angular-material.css (line 2798):

@media (min-width: 600px) and (max-width: 959px) {
[...]
  .layout-row > .flex-sm-100,
  .layout-sm-row > .flex-sm-100 {
    -webkit-flex: 1 1 100%;
        -ms-flex: 1 1 100%;
            flex: 1 1 100%;
    max-width: 100%;
    max-height: 100%;
    box-sizing: border-box; }

This code applies on child elements on a medium screen, and doesn't apply on a small screen