Okay did some brief testing with 32 bit 4.0 on Win 7.
It does appear to be an issue with spaces in the filenames. I first started an empty book and added some random text to the initial file. Added a new item and added more random text to the new file. Then I picked a random spot in the first file and did a chapter split. Everything split okay and the new file appeared right after its parent as expected. Saved and reloaded and everything looked fine.
Then I changed the file names of the second and third files to include spaces, went back to a random spot in the first file and did a chapter split and the files were no longer in expected order. I then saved and restarted and reloaded and the new file and all the text in it were missing.
Tried a few other things and each time, seemed fine if the files names didn't have spaces and started acting strange and losing data if they had spaces.
Of course a LOT of my books have spaces in the filenames...
