If the Internet Explorer has to display animated GIFs, it may happen that it cut’s off some pixels from the bottom of the image. To make the confusion even harder, it does not cut off pixels from all animiation frames but only from a some of them.
The same animated GIF might be displayed fine in other browsers such as firefoy, chrome or even opera.
The problem is reasoned by the configuration of handling none active image frames. There is a configuration for each frame of the animated GIF to set, if this should be present in the background or not if it is not active. For example in the animation View of Photoshop, you can choose for each frame seperatly if this frame should be removed or not, or let Photoshop decide this automatically. By default, this is set to not remove inactive frames and Internet Explorer might cut of some pixels from the bottom of the active frame. This leads to some pixels of the inactive frames beeing displayed instead of those of the active frame.
So as a solution, change the setting of all frames, to remove them when they are not active. This will solve your problem very easily.