I have just tested your scenario on my own copy of TTD.  Presumably you are referring to the Tslip entry window in the Forms view of the software.  When you enter the Actual dividend, the Taxable dividend, and the Dividend tax credit, the display will show the sum of those three numbers...which is what that window indicates.  However the software will properly allocate the Taxable dividend amount to line 120 of the T1.