Mmm, very puzzling. I've looked at the code for the gallery index.php page that svManager is generating and it looks perfect. So it seems to be a problem with SimpleViewer itself. Have you done anything to change the viewer.swf file?
You could download a new copy of viewer.swf from the Airtight web site and substitute it for the one in the gallery to see if it makes a difference.
Other than that it's down to old-fashioned minimum-case fault finding. That is, creating a test gallery with the problem and trying to eliminate the variables that might be causing the problem one by one.
We can already eliminate browser and operating system. I'm seeing the flashing caption in IE7 Windows and Firefox and Safari Mac.
It might be worth a post in the SimpleViewer forum.
SimpleViewer Support Team.