Ok, I have 2.5.14 and this problem still happens for me. It was so irritating that I just can't use background images. Even though I'd like to. There seems to be some magic key sequence (that I haven't quite figured out) that will get it to stop blinking. But then as soon as I do something it comes back. It seems to blink in synchronization with the clock ticking each second.
The blinking occurs when the TD sets the background image, which previously it did every update to the screen, which occurred on average once per second. By setting the background, it is simply telling Internet Explorer "this is the background image". IE, and most browsers, are smart enough to notice when you set a field to the same value it currently holds, and won't take any action when you do (such as re-render the screen). This worked great for years. Then, with IE 9, this changed ... at least with respect to the background image. When it is set, IE always re-renders it, even if the value is unchanged. Not only does it re-render, but it re-renders first with no background, then it re-renders with the background. Thus the "blink". This is an IE bug. TD's workaround is to simply be smart about setting the value. If it hasn't changed, don't set it.
Having said that, and having not heard a word on this issue since the release of 2.5.12 (other than the report that started this thread, which turned out to not be an issue) which was nearly 2 years ago.
I should also mention, that this happens when I've got two external monitors connected to my laptop. I can't seem to make it happen when I'm using the builtin screen on my laptop.
Thanks for the info, although I cannot imagine why this would make any difference. So, has this happened as long as you've had IE9? Does it blink with all/any background, or just a specific one? Can you send me your exported layout so I can try it? Or better yet take a backup, on the Database tab, and send me the backup file?