Faint outline of cube faces showing in HTML5

There is a faint gray outline showing the edges of the cube faces in the latest panoramas I have made. This outline only appears in the HTML5 versions not the Flash versions (playing back in Safari). I have re-checked the dimensions of the original equirectangular files and they are correct and because the Flash versions are working, I suspect the problem lies elsewhere. Has anyone else had this issue or know why I'm getting this result?

Neil

Thanks for replying Klaus. I'm using krpano 1.1.7 - from my limited testing the lines are only appearing when viewing the HTML5 version using Safari on desktop computers (Mac OS) - I can't see the lines on iPad or iPhone. The lines don't show on all the cube face edges, just one edge of the top face for example. The same result is showing on older versions of Safari that I have set up here: 5.0.6/5.1.7 and a later version 7.0.3.

Best Regards, Neil