Another issue regarding putting dye black ink in the larger cartridge intended for pigment ink:
The major advantage of pigment ink on plain paper is that it won't smear or run if the paper gets wet. However, recently many suppliers of plain paper now give them a ColorLok treatment which significantly reduces the smearing and running of dye inks. So if you use dye ink exclusively in your printer and use plain paper with ColorLok, you may be able to get the significant advantage of pigment black ink without using pigment ink.
Furthermore, if you use a plain paper with ColorLok, there is one significant disadvantage to using pigment black ink which is that it will smear if you use a highlighter on it. So I can see that using plain paper with ColorLok and switching to pigment black ink has several advantages.
However, I would recommend purging the cartridge before switching from pigment to dye ink. I once added some dye black ink to a pigment cartridge thinking it might help unclog some nozzles but it made it worse. It's a good precaution to take even if it doesn't matter.
Is this behavior "using all inks instead of black for Duplex" true for all Canon printers?
I bought a used Canon Pixma iP4200 for printing double sided text documents with some charts and images (manuals for workshops etc.) as I assumed this printer will use the pixgemented black PGI-5 for text and the dye CLI-8 for color parts.
Not 100% but I think thats the way it works. Single side, Pigment. Duplex, Dye.
There was a long thread about that a while ago. SOmething to do with preventling or reducing one side of the printed text being visible from the opposite side.
Chances are it's the same for all Canon printers but I don't know if everyone has reported their experience with all the different printers. It's pretty hard to tell unless you do the definitive kind of test that I did and reported on in the second answer of the FAQ on "What is the difference between pigment and dye based ink?" Click on the Inkjet FAQ's link at the top of this page to get to it.