It actually had nothing to do with Metadata 121 (the Boundary), MetaData 534 (the new 'kpr') and nothing to do with the new 0x0080 bit in exth_flags.
It was actually the exth_flags 0x0800 bit that seems to indicate that the shared resources in a combo mobi are stored in this header. We never bothered to remove it when we split the combo mobis because it never bothered anything and we were never 100% sure of its meaning.
Now it does matter for KindlePreviewer 2.8. So we need to zero out bit 0x0800 in the exth_flags in the split mobi to say there are no longer any shared resources (images, etc) in the mobi 7 part of the file.
I have modified mobi_split.py to reflect this change and have uploaded it as mobi_split.py.zip.
Please download this and use it to replace the older mobi_split.py file in the KindleUnpack_V61/lib/ directory. Then give it a try and let me know if your troubles go away. If so, we will add it for the next release of KindleUnpack.
Thanks for your bug report and especially the test case.
Last edited by KevinH; 02-22-2013 at 10:00 PM.
Reason: fixed typos