Even though the span which is a child of anchor has some minimum height because of the text it holds, the anchor as such doesn't has any height in IE. Because of this, whenever you hover over the text, the tooltip doesn't appear. To verify the same, execute the following code snippet in console
document.getElementById("element's id").offsetHeight // will return 0
This is a bug in IE and workaround would be to do something like following:
a[title] span {
display: inline-block;
}