Where does the $1500 extra income show up? In particular see if it was added to line 1 of form 1040, with a notation SCH1500 on the dotted line to the left. If so, TurboTax has treated the $1500 scholarship as taxable income because it used all $4000 of the tuition to calculate the Tuition credit, either on your return or your parent's return, if you are a dependent.
Also look at lines 20 & 29, this is where the education credit will appear (if you qualify).
