Is this a new "feature?" I have a 3880 and regularly print on both matte and glossy paper. I've never noticed (I'm pretty sure) that the printer has failed to switch with low ink warnings showing.
I have never encountered the issue before on my 3880 either, and as i noted earlier, I don't have a P800, so I cannot confirm whether the P800 with its bigger volume cartridges will negotiate the low ink status PK/MK swap differently than the P600 with its much smaller cartridges, but here is a shot that shows the P600's low ink warning "feature". The image showing the yellow triangle (very low ink) on the yellow cartridge was recorded with an iphone right off the LCD panel of the P600 printer,and also shows the warning you get when trying to switch black inks. Note in this very current photo of my P600's status that both PK an MK are quite full, thus proving that any low cartridge not just a low PK or MK can trigger the P600's refusal to make the Black ink swap.
The other two attached images are screen shots of the utility panel you can check on your computer. In one image you can see that four inks are low including the PK ink, but none have posted that yellow triangle warning yet, and in the other screenshot the low PK ink was replaced (but didn't solve the switch refusal) while the cyan cartridge had next reached the yellow triangle low warning. What this all means is that there are actually two "low" levels, the really low level where a cartridge shows a yellow triangle warning and another lesser low level that still has enough ink not to trigger the triangle warning but still too low to allow the swap. Lastly, it can be seen in these photos that the cartridges really don't stay in syncronization, so just about the time you get one replaced another is now heading into that low zone which is going to negate the opportunity to make a black ink switch.
While I may try to study this whole low ink cartridge temporary removal and then replace strategy as a way to circumvent the ink swap refusal when you only own one printer, I don't have high confidence that constant swap outs and set asides of opened ink cartridges is a very good idea. But it's worth understanding as a possible work around to the black ink swap conundrum, so I will probably give it a try.
To me, if you are a serious printmaker who wants very best image quality in smaller sized prints, The P600's 5760dpi setting does deliver subtle yet noticeably superior image detail compared to 2880 dpi, albeit at significantly slower print speed. Hence, even if I owned a P800, I'd still be tempted to have the P600 in my studio as well. Thus, the ideal situation if you want to print regularly on both matt and glossy media and if room space isn't a problem, is to own two of them, one dedicated to PK and another dedicated to MK. Another advantage of that approach is one can swap the mostly still full PK and MK cartridges periodically and directly between the two printers (ie. not have them lying around outside the printer), thus effectively managing any potential concerns about shelf life of the lesser used black ink in each printer.
cheers,
Mark
http://www.aardenburg-imaging.com