Hi, I don't really follow exactly what is going on with your tests, but perhaps I can offer a test for you to try.
If you think that the printer itself is the problem, you might try removing it from the test. It doesn't seem to be well known that you often have the option of "printing to a file." When you go to select the printer to use, you select a "file," or whatever the exact terms are. Then, with this new "device," actually a file on your computer, set it up with the same "printer profile," etc., as you have been using with your Pixma printer. Give it a filename that you can find easily in a search, as it might be buried somewhere in your computer system.
After doing the "print to file," open the file an see if the artifacts exist in it. If they DO then you know that they are not a result of the Pixma printer.
FWIW this print-to-file image will have the pixel values changed, to the pixel values that would have been sent to the Pixma printer. But... the appearance of the file (in a color managed system) should appear similar to the original file. This is because of the complicated operation of the ICC profiles. A printer profile has a backward-looking set of translation tables, which the system knows to use in this case. So even though the pixel values are now changed, a color-managed system will attempt to show the file as it SHOULD appear on an actual printer. Out-of-gamut colors will be clipped according to the limitations of the printer. For your purposes it might be worth looking at the actual RGB pixel values in the output file; I dunno if they're useful to you or not.
FWIW I've never used Qimage; it's possible that it might try to defeat the test I've described. If so you might try printing directly out of Windows. I don't recall exactly how, it might be a right-click on the image to start out. I'm sure a number of people on this site will be glad to step up and explain the process.
Ps, I think the term you meant to use is "out of gamut," not gamma. (Gamma is normally used to describe the slope of a line, as in measuring contrast. Whereas "color gamut" means, more or less, the range of color strength that a system can work with)
Best of luck with your experiments.