ACR 11 - weird transparent red / pink box shows up on images sometimes

We updated ACR, Bridge and PS last week, since then we have seen a weird redish or magenta-ish box show up on top of the image sometimes - I think we have seen it on 10-12 images so far (out of a thousand maybe). I can't reproduce it unfortunately.

It will show up on the rendered jpeg. The images we are working on are jpgs to begin with- not RAW files.

It will go away if we notice it in ACR - just fiddling with some of the sliders will make it go away.

It shows on both the thumbnail and the main image.

I just saw it on one image where the pink box showed for a split second and then went away. We kept going back and forth between images and it kept doing it.

The pink box seems to show up on top of either skin tones or reddish clothing.

We are a photo lab, so they are not my images, it has happened to multiple different customers images.

(white box over thumbnails is on purpose to protect the innocent)