Maybe it is one of these causing it:

Note: Per 1040 form instructions for line 23, qualified educator expenses are reduced by the following:

    Excludable U.S. series EE and I savings bond interest from Form 8815
    Nontaxable qualified tuition program earnings or distributions
    Any nontaxable distribution of Coverdell education savings account earnings
    Any reimbursements that were not reported to you in box 1 of your Form W-2