I tested printing quite a bit of different documents with an application I have here and all of them get printed correctly with the patch. Before the printed pages were just blank. What do you think is better for a user?
It's not good if things work by coincidence in one case that's important to you, and then we can't fix other cases later (or we can't fix other cases without breaking yours).
I don't understand your objection, nothing prevents you from improving my patch. Printing something is still better than printing nothing, consdier this as adding a partial implemenation in the place of a stub. GdiAlphaBlend is not supported by printers, that's a matter of the fact, using StretchBlt for now is better than doing nothing and even not printing a FIXME or returning an error to an application. Feel free to implement it differently, until that my implementation is suffice for many applications.
Printing something is worse than printing nothing when it's a giant black box that happens to contain the thing that was supposed to draw, and that will start happening if you make this change. And then I won't know how to fix it.