rtl mis-parses border-color in a mixin

[Jonathan Cohen]

I'm using some polymer components in my electron app. We have some CSS that looks like:

paper-input {
   margin-top: -8px;
/* some other stuff */
  --paper-input-container-underline-focus: {
    border-color: white;
  }
/* more stuff */
}

After applying postcss-rtl it's split into two different paper-input blocks and the mixin is removed

paper-input {
  /* some stuff */
}
 paper-input {
  margin-top: -8px
   **border-color: white;**
}

The stray border-color goes away if I change that to be "color", but that isn't the right property for the job. If I put multiple properties alongside the border-color then just the border-color gets split out and the other properties remain inside the mixin.

I'm currently using rtl:ignore as a workaround since the styling is independent of direction, but someone else may have a different experience.