OK, I have narrowed it down to the form TP-726.20.2-V. This form is the most visible example of Intuit stupidity and stubbornness, as year after year they simply refuse to get it right. If I remove the values from #34 and #54.1 (which come from the previous years) and, effectively, reduce the line #75 to $0, it seems to work around the issue - at the cost of extra $$$$ paid to Quebec, of course.
So, worst case, I can go without this form at all and then file the paper adjustment...In the past years, this form worked at least for the values from T-5013/RL-15 forms, but this year it seems they have broken even that.
