Characters change case in PDF

Hello,

I'm not sure which forum I should be asking this question in, so apologies if I've chosen incorrectly.

A couple of days ago, from InDesign, I exported to PDF the index section of a book I've been working on and emailed that PDF to the author.  When I look at the PDF on my computer, it looks perfectly fine.

When he looks at it, certain upper-case characters have been transposed to lower-case - it's always the same letters and only occurs when the character is in the standard font I've used (i.e it doesn't happen when the same characters are italicised). From what I can gather, aside from that it happens in every instance the particular upper-case characters appear.

I wondered if it was a font-embedding issue, because I was viewing the PDF on a computer where the font is installed and the author would not be, but if I copy the PDF to a laptop of mine which doesn't have the font installed, it still looks fine there too.

On the other hand, using the same computer that I used to create the PDF in the first place, if I open the PDF in Acrobat and export the text to a Rich Text format file, the resulting .RTF does exhibit the case problems. This last thing isn't specific to Acrobat; if I open the PDF in Foxit Reader and export to plain text (the only option I have), again the same problem occurs.

I have InDesign CS5.5 (7.5.3) and Acrobat X (10.1.16). The latter informs me that the PDFs were created with Adobe PDF Library 9.9.

Any ideas?