I have nothing to suggest as a solution, but I have to mention something I noticed.
That scrollbar in the middle seems to be opera's native scrollbar (the grey one), while the one on the right seems to be the site's skinned scrollbar (the blue one). On the other hand, opening your site on my pc, shows only the native scollbar and on the right side.
One thing I can imagine is hardware acceleration? Do you have hardware acceleration active? And what gpu are you on?
I am on debian testing x64, with an old 9500gt, running the nvidia 340 legacy driver and with hardware acceleration enabled.