There have been numerous reports of similar problems when printing to the latest Epson printers.
That thread is about problems trying to send unmanaged data to the printer -neither Photoshop or the printer manages color. (Of course you know that ... you started the thread which helped identify the problem for some of us.)
For the OP, it seems that under OS X 10.5 and CS4 if you set the printer to manage color, and turn off color management in the printer driver, the OS is still doing something with the color. This makes it very difficult to print targets for creating profiles. However, I believe for most users when having Photoshop manage colors, the results are what we expect, and indeed the driver color options of colorsync or Epson color controls are actually disabled.
I have seen reports by some having this problem, but it seems most do not. I don't recall anyone that has actually nailed down what is different about their system that might be causing the problem. It most likely is related to the same bug, but some how it only shows up under certain conditions.
As far as fixing it, a couple of ideas. First I would use the printer drivers installation program and deinstall the driver, then reboot and reinstall. Could be a complete reinstall of system software ... and if you do this I recommend you use the custom settings and turn off all of the OS X printer driver installs, so the OS doesn't install drivers for your printer. Then reinstall the latest drivers. Also, some have had success using the colorsync utility to set the default profile for the printer to the profile they are printing with. There is also a possibility the profile needs repaired. I don't use a z3100, but it seems the printer stores profiles so when letting the printer manage colors does it use the profile stored in the printer?. Could it be the profile on the computer somehow isn't the same profile? (hey ... wild guess here. As I said, I'm not quite sure how the z manages and uses profiles. Plenty of z users around, maybe they can comment on this)
Just a couple of ideas.