Couple of thoughts...
Sony Reader Fan, thank you for the clean epub -- I'll post a screenshot of that, too.
JSWolf, thank you for the embedded file -- I'll load that up tonight, take a picture, strip the fonts out, take a NEW picture, and then post both pictures for comparison.
Jack, yes, you read correctly -- any book that does NOT have embedded fonts is
bolding it up. I'll remove that .calibre tag -- I had copied this from another thread, so I'm glad to hear that's not necessary.
I'm very worried you may be right about PRS+ causing everything to be bold. I certainly don't know how to fix THAT.