Originally Posted by Perkin
I 'm not sure but I think there was a bug in Sigil when if it splits a file, the link didn't get correctly updated unless it also had the filename.
(Not sure if it was a Sigil bug, or if it was, if it's been fixed)
I don't remember this bug (and I usually remember bugs). It was either reported and fixed a long time ago, or never reported at all. Try to make a test case and then report it if you succeed.