Hi there! 

Hope you are doing well. That is a fantastic question! As you live in BC while working in Quebec, I am going to make the assumption that you work remotely. As of this, taxes are collected based on your employer's province but payable based on the province where you reside in, which is BC. The overpayment will get rectified once you submit your 2023 tax return. 

This is correct, but unfortunately doesn't answer the question. Why is Turbotax adjusting income taxes overpaid including EI/QPIP, but not CPP/QPP.

Can you please make sure that you entered your province as BC and your T4 you entered Quebec.

On my T4, province of employment is QC, but yes BC was selected as my province of residence. As mentioned, income tax and EI have been readjusted correctly. It's only the CPP that is incorrect. 

I think there's a calculation error on the form RC381. Line 49 says 4038.40 but it should be 3,754.45

Line 49 is the sum of lines 45 & 48 which equals $4038.40, that form is correct.

Go to the left-hand side of your return and click on the drop-down arrow below the amount of refund/owing you have- then choose View detailed tax summary line 44800- CPP overpayment.

Line 44800 isn't shown. but I do see line 45000 for Employment insurance overpayment $228.14. As I mentioned, income tax and EI are adjusted correctly, but not CPP.

Do you mean that there is a zero in that box?

I see line 43700 and 45000 but I do NOT see 44800 whatsoever (it's just not there at all).

Can you see it, when you do the steps above?