I had a chance to take a look and I can see what the problem is but not why it's happening.
Part of creating the KePub file, when you request hyphenation support, is adding a CSS file to the book, and editing the inner HTML files to include a reference to that CSS file. The location of the CSS file is /kte-css/hyphenation.css (off the root of the ePub file). In the log you sent me showing it working, the paths look correct:
Code:
Input file: OEBPS/Text/@public@vhost@g@gutenberg@html@files@14105@14105-0-0.txt.html
CSS relative path: ../../kte-css/stylehacks.css
Home directory: C:\Users\Juergen
However, where it isn't working:
Code:
Input file: OEBPS/Text/@public@vhost@g@gutenberg@html@files@14105@14105-0-0.txt_split_000.html
CSS relative path: ../../../../J�rgen/Desktop/kte-css/hyphenation.css
Home directory: C:\Users\J�rgen
So something is indeed different between these computers. The formatting of the home directory suggests either there's a locale difference (which I don't know how to check on Windows) or the actual home directory name is different. On the working computer, where the CSS relative path is correct, you aren't using a different temporary directory; on the computer where the CSS relative path looks wrong, you are. I tried on Linux setting a specific temporary directory and it worked fine, so either that's not part of the problem or there's a Python bug specific to the Windows version of Python.