It appears that Calibre messed up your valid epub. I have no idea why the K3 appears to be displaying the embedded fonts and the Paperwhite doesn't, but with the K3 font embedding can be hit and miss anyway.
Since earlier versions of the Calibre font embedding code were buggy, downloading the latest Calibre version and re-embedding the fonts might do the trick.
Also, if you're getting strange results after Calibre epub conversions, try checking the epub generated by Calibre with
epubcheck online to make sure that's still valid.
Since epubcheck error messages tend to be a bit cryptic, you could also download
Sigil, open your file with it and click the big green checkmark button to run the integrated FlightCrew epub checker. (Your Calibre-converted epub failed both tests.)
BTW, if you encounter further problems with Kindle books, you may want to post your questions in the
Mobi forum.