First, are you using the latest version of ItemRack? Do you have any other addons that touch the character window or your tooltip? You may just need to disable your addons one by one (or in halves) until you find the culprit.
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"You'd be surprised how many people violate this simple principle every day of their lives and try to fit square pegs into round holes, ignoring the clear reality that Things Are As They Are." -Benjamin Hoff, The Tao of Pooh
Good. I thought that was the error from ItemRack when 2.3 hit, but wanted to be sure.
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"You'd be surprised how many people violate this simple principle every day of their lives and try to fit square pegs into round holes, ignoring the clear reality that Things Are As They Are." -Benjamin Hoff, The Tao of Pooh