You have this in the head of your page, which is overriding the normal body background, placing a background image on the body that is too short:
background: #B7B79E url(../img/bg.jpg) repeat-x;
I don't think the effect has anything to do with animated gifs.
Rather than have such a tall background image, it would be better to set a background color on the body like #faf9e5 and then just have the green part or the background image with the stripe at the bottom as your background image. Then, if a page gets really tall, you'll have no issues of getting the green/gray background at the bottom again.
As for seeing the effect on another page, I'm sure I did, but I can't find it now. May be going mad.