So, I worked through this with a TurboTax Advantage expert.
To avoid overcounting, it's necessary to leave amounts for property taxes and mortgage interest blank in the deduction section, since these have already been entered in the Income part of TurboTax's EasyStep. And while I overlooked the note telling me to do so about property tax the first time through, there is no such built-in advice about mortgage interest.
The comment below about pro-rating the share of the house is relevant for folks who began or ended renting part of their house during the tax year, or who took personal days in their rental. Both cases are options in the income side of TurboTax.
