I'm going to assume that it is an issue with the eq2ui_fonts.xml file. I have used a maintained window that had text for the spell name, target, etc...and when I used the eq2ui_fonts.xml that came with it (it was from 2005 as well) the tooltips stopped working. If I deleted the file, the tooltips would work, but then the text in the effects window stopped working.
Someone who knows more about modding than me can probably help you out, but what I did to fix it was open up the UI in the UIBuilder and find another window that used a different font, then edited the maintained fields to use that font rather than what it was set to.
Works like a champ for now