Hmm, that's an interesting one. The doubleslashes shouldn't cause a different image to show up. I'd have you open a trouble ticket but since you said it happens very rarely, I may not be able to reproduce it and fix it.
The next time you notice it, can you post the full actual image and incorrect image, so we can see real images being displayed? If you'd rather keep the images private, then you can PM me with the info.
