Thanks a lot for all comments and suggestions. They gave me lots of ideas of how to tackle similar issues in the future.
From a legal perspective, would it be okay to remove the DRM, which would be necessary when converting a DRM protected book from EPUB to MOBI and back? ;-)
Fundamentally, a product should do it's job. An e-book reader has to display books that comply with the format. If it doesn't, it has to be fixed in time or I won't buy it. I will not spend my time working around the problems that where cause by the party who got the money. The reason why I put so much effort into figuring out what causes the crash was that Sony support indicated that it's my fault because I want to display something that's not covered by the standard.
Now I've got a lovely Pocketbook 623 (which also has shortcomings, but it does it's primary job). Problem solved.
I used the EPUB validator on
http://validator.idpf.org/ to check the format. I did not complain.
When describing the error case, I was not specific enough. The problem is a line consisting of a single space somewhere between the <pre> tags. Empty lines occur quite often in program code listings - guess what kinds of books I most frequently read.