Did you manage to test this? I think ufile has a bug around this, or at the very least, isn't very well designed to allow the full donations amount to be used to reduce both federal and provincial amounts beyond the amount required to bring the the federal owing to zero.
I could find nowhere specifically outside of the Schedule 9 - Donations and Gifts how line 1 is calculated. I can infer though that the amount entered here is the amount required to bring the federal owing to zero. However, line 1 from Schedule 9 is also then used on the BC Provincial worksheet, even though there are more donations available. I understand it's probably better over multiple years to carry over anything not used to reduce bother federal and provincial taxes, since anything used to reduce only provincial amounts would resulting in less reduction per donation. However, having the choice would be nice.
This is further an issue when there are other deductions. For example, I actually end up with MORE tax owing when I deduct medical expenses. From what I can determine, the medical expenses are used first to reduce the federal amount before the donations. As such, the result is that Line 1 of Schedule 9 actually requires LESS donations to bring the federal to zero. This then results in the smaller amount being used for the provincial tax calculation, and since less donations are used (more are carried over), the amount owing for provincial for this year is actually more!
