Maxify PGI-1200 Refillable Cartridges - Leaky Blue?

[nobb]

I suppose this is what happens (when you do not print enough).

As @Artur5 found out, the printhead has a buffer with a few ml ink for every colour. Most of the time the contamination does not rise into the cartridge.
Why doesn't this occur with fresh OEM carts (or does it) ?
Maybe they are filled with a certain negative pressure ? What is the function of the ventilation aperture of the cart ?

I've taken apart the print head before for manual cleaning, it's moreso that there's a bit of volume inside where old ink from each color could reside as a "buffer". The print head PCB and head can be unscrewed and separated from the cartridge carrier and there's some seals inside, but otherwise there's no fancy venting or whatnot within the print head assembly itself. That's why I presumed the only way for contamination to occur is for one color to seep out through the nozzle, then get absorbed into the adjacent nozzle. I agree in that it would be very unlikely for the contamination to seep all the way back into the cartridges themselves.