I wasn't 100% sure the best place to post this, but since this is an issue that's showing up on my Kobo, I decided to start here.
In my sideloaded books, if a chapter title has a colon in it, the space after the colon is removed from the in-book header where it shows the chapter title. So instead of saying "Chapter 1: Title" it looks like "Chapter 1:Title". This issue also shows up in the footer menu's table of contents, but not in the ToC in the book itself. I've also checked the "Edit ToC" interface in Calibre, and that doesn't show any missing spaces either.
Any idea what could be causing this?
If it helps, here's one of the sideloaded ebooks (scrambled):
sideloaded - author.epub