Dear Brlowe. Thanks for the photo! This is a problem with all reset chips when you have selected one black and you are going to go to the other (in this case MK). What epson does is require the use of a new cartridge but what you need to do in this case, is print a few more PK prints until the PK resets to full. Then you can switch to MK.
We have a notice about it on our product page although you probably got these chips before we had placed the warning up there.
If your Photo Black ink reading is very very low on the chip and you switch your printer to Matte Black, you won’t be able to switch back to Photo Black. Normally at this point, Epson would force you to buy a new cartridge. When your Photo Black is reading low, keep printing until it resets, top it off, and then switch to Matte Black!