Strange new problem - print color difference between CS3 and Lightroom

I've been using CS3 and Lightroom for months now, with a Canon MP600. Print quality has been quite decent, with accurate colors from both apps.

Just in the last few days, photos printed from CS3 have taken on an under-saturated look with a bit of a greenish cast. I first noticed it when I went back to print a few more copies of our xmas card pic. I printed 70 copies of this photo in mid-December and they looked great. The other day, I opened the SAME file, with no modification, and printed a few... and they have this undersaturated greenish cast. I then printed the same file from Lightroom, and it looks just fine.

I haven't changed any pertinent settings. Working profile in CS3 = ProPhoto RGB, to match pics imported from LR. I convert to Adobe RGB before printing, and use the Adobe RGB profile on my printer; it's always worked great. I have plenty of ink. I'm using the same paper. Color spaces, rendering intents etc. have not changed.

Oh yeah: I can actually see the change take place on my monitor in CS3. In the printer dialogue I select "preview before printing"... then, when the preview pops up showing a borderless print, it has a really under-saturated look. This never used to happen, and that's indeed what the print ends up looking like.

WHAT HAPPENED???????

Thanks for any input...

Ink levels in the printer are all good?

Nothing lower than half... and prints from Lightroom look good.

Maybe something went stupid in your CS3 preferences? I've read that that can happen...

That's what I thought too... I mean it almost has to be since it's a problem isolated to CS3. I just can't figure out what!

Well now this is interesting... I just realized I'd taken a series of Adobe updates the other day. I just reviewed the history of CS3 patch. Among other things, it does this:

# Photoshop now turns off Windows ICM (system color management) when "Photoshop Manages Colors."
# Print color matching has been improved.

Well, Photoshop isn't managing colors in my case... but what's that "print color matching has been improved"? Not in my case!

Hmmm....