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This fix worked for me on my iP4 running 5.0.1.

The only problem I have is that iBooks 1.5 on both my iPad 2 on 4.3.3 JB and the iP4 on 5.0.1 JB does NOT like you to change font size. At anything other than the default for a particular book, it loses its place in the book at chapter breaks. Drives me crazy.
 
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