As suggested, I have contacted your help line, and was told that the program is computing the amounts correctly and that only the percent of space and not also the percent of time is to be used.
I have just contacted Revenue Quebec, and they have told me that your interpretation is incorrect. If a room is only used part of the time for working from home, then that percentage of time must also be used to compute the deduction for working from home.
As an illustration, if for working from home you use 200 square feet of your 1000 square feet appartement (20%) and you use a common room (e.g. dinning room) for 17 hours our of 168 hours a week (10.11%). Then the percent of your rent, utilities, etc... that you can deduct is roughly 2% - not 20% which is what your sheet Q777 does. The amount turbotax computes is correct for the federal forms, but incorrect for the Quebec form.
I suggest you validate this with Revenue Quebec and update your program.
