I came here with the same issue:
"//" appearing after image_cache when pointing to new image.
Now, it seems to work in IE and FF so far, in that the images appear and load quickly, but I am not a fan of irregular code like this. Is there a workaround or a way to fix it quickly across all instances?
The code on the page just references "image_cache" as the destination which is what I first thought the problem to be.
Any ideas? or no cause for concern?