What preset were you using? Most likely this is inconsequential.
I'm using a MagCloud PDF export preset 8.25 x 10.75 Standard preset
What is a MagCloud preset? What are the actual settings under color management?
Like Peter, I hadn't heard of MagCloud.
Apparently this was a print-on-demand service from HP.
However, they were taken over by Blurb in May 2014.
You might want to download the InDesign PDF preset for Blurb from the Blurb website.
Are you using ver.4 icc profiles for your images?
From the little I have read, some ver. 4 profiles may be troublesome, but also that ver.4 files are not widely supported.
The support issue may be why they are converted to ver.2
I discovered the issue was with some of the images themselves. Once I replaced them, that solved the problem.