SL3 issue: "Zoom Picture" is adding a grey border around the image

I'm on the latest version of Storyline 360 and the bug is still there (after 4 years!). It is inconsistent, sometimes it puts a grey border on, sometimes it doesn't. As my images are on a plain white background if I apply a Storyline white border to the 'zoom' images it seems to resolve (apart from having a white edge, which is preferable).