You have two calls to show(), one of them is delayed a lot, the animation you have also takes time, so what happens is that you first initiate a wrong show() (without the timeout suggested in the sticky thread you linked), the tooltip starts to show, animation takes time, after that the delayed show is called, animation starts again, the tooltip's element is positioned below the mouse pointer, it starts animating and at some point the mouse is again over the link, the mouseover fires, the tooltip shows and so on and so on.
radTooltip1 = $find(
"<%= RadToolTip1.ClientID %>"
).src = imgPath;
You can also try removing the animation, because this can invoke more calls to onmouseover.
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