Thank you very much for the testcase. There are two differences that I can see:
1. The exth_flags now have value 0x08D0 instead of the more normal 0x0850 for the Mobi 7 part. I have never seen that 0x0080 flag bit set. I am wondering what this new flag means. Given how simple this test case is (no fonts, no images, no anything really) it really could just be that the source zip and build log are included in the Mobi 7 part.
Interestingly, the Mobi8 part exth_flags do not have this flag bit set. So it is indicating something for only the Mobi 7 part and there really isn't that much different between the two versions.
2. There is a new metadata item 534 which seems to be the string 'kpr' which for some reason I thought meant kindle print replica. I can not figure out why that metadata item is present. And what 'kpr' means. I can even find it in the build_log that is stored inside the test case. Anyone know what 'kpr' stands for since it is obviously not a 'kindle print replica' in this case?
Of course it could be none of these differences, and we may need to start removing the Metadata 121 item (the Boundary Section value) in the split Mobi 7 part instead of just setting it to 0xffffffff as we did earlier.
Hmm ... I seem to be having trouble getting KindlePreviewer 2.8 for Mac downloaded. Once I get it I will try changing each of these issues in the split code one by one to see if it is the metadata values or the extra 0x0080 flag in the Mobi 7 exth_flags part that is the problem. I will let you know what I find out.