Transparent areas change shade of solid color areas behind..

I have some PNG images with transparent background in my Pub 2007 document.
Some of those transparent areas overlap a colored textbox behind them.

When I print to PDF (using either Pub 2007 Print As... PDF (commercial
printer settings) or print to Nitro PDF and then print the resulting PDF on
my HP 3600n color laser printer the area where the transparency overlaps the
colored background is dislored (slightly darker). You can't see it on the
screen but it's quite apparent in the printout. It's exactly where the
transparency is.


What I 've tried:

1. Redid the background transparency using Microsoft Picture It to manually
trace the object and cut out the background. Saved as PNG.
2. Tried inserting that object and printing (as described above). Problem
present.
3. Tried recoloring the background to RED and then using the Pub2007 "Set
Transparent Color", set to the red background. Same result.

4. Tried Right-clicking on picture and "Save as picture " (PNG) and
reinserting that into document. Same results.

Any other ideas?