I think this broke a couple of years ago, but apparently I never reported it, and no one else did, either. The call used to have its line get a blue background, but now all that happens is sometimes some mildly-orange pixels appear to the left of the call:

I think it might have appeared around the same time as the version of Qt used changed, but it was so long ago that I don't remember whether I confirmed that or was just guessing.