@dandsrobert I gave up on the online version, deleted my return and I ended up paying for the whole program download and that calculated things correctly. So that wasn't ideal!
I wonder though, did you click the "I used the calculator" option when you got to that point? That's what I did in the online version and just input the appropriate numbers for the appropriate lines. But when I used the full downloaded version of TurboTax, it didn't give that option - I had to enter all of the amounts (i.e. square footage of home, office, bills etc.) for it to make the calculation itself. So I wonder whether it would work in the online version if you don't say you used the calculator and enter the amounts manually? Maybe something to try if you haven't already.
Either way, given that the online version has the calculator option available, it should be addressed by TurboTax. I wonder how many people just assumed that they weren't getting anything extra back using the detailed option, or didn't notice that it didn't change the return amount and continued on and submitted their taxes? I hope that the numbers at least are in their returns somewhere and that the error gets picked up by the CRA and returns are adjusted accordingly. It's a pretty fatal flaw in the software in my opinion.
I called their customer support and got an answer.
I had imported the T4 amounts from CRA but what they don't tell you is that you have to in to the T4 slip, edit it and select the "YEs" i am claiming amounts for home expenses option.
Once I did that, the amount showed up on line 22900