Ok, so I think the title attribute is added in via a function in one of the vBulletin javascript functions which specifically copies alt text to title text. That means it's applying the title attribute after the page source is downloaded, explaining why there's no title in the source code and why the title appears if you inspect the element. 
EDIT: Ok, yes, these two functions exist in <a href="http://forums.eyesonff.com/clientscript/vbulletin_global.js">the vbulletin_global.js</a> script. Here you go:
PHP Code:
// Substantially deobfuscated :p
function child_img_alt_2_title(A) {
var C = A.getElementsByTagName("img");
for(var B = 0; B < C.length; B++) {
img_alt_2_title(C[B])
}
}
function img_alt_2_title(A) {
if(!A.title && A.alt != "") {
A.title = A.alt;
}
}