This is an exceptional case, because TurboTax automatically subtracts the HSA distributions (as you see) from Medical Expenses, even though the expenses were in a prior year. This can end up unnecessarily reducing your Medical Expense for 2018.

To address this issue, go to the Medical Expense interview (the one for Schedule A expenses) and navigate to near the end. Where you have a chance to enter other or miscellaneous expenses, enter one with the description of "HSA reimbursement amount" and the amount of your distribution. This will cause your Schedule A calculations to be correct.

Yes, this leaves open the issue of how do you handle the fact that you got reimbursed years later for medical expenses for which you weren't reimbursed in that year so deducted. In theory, if you were able to deduct Medical Expenses in 2017, then you should go back and amend your 2017 return to remove the amount of the expenses that were reimbursed in 2018.

[edited 2/18/2019 2:59 PM CST]