It is not syntax related. It is related to how many different inflection rules are needed.
So languages that make heavy use of prefixes and suffixes with a large number of rules means one entire mobi section can't hold enough and multiple mobi sections are needed.
So I will need access to one of the broken dictionaries to figure this out.
Same thing for Japanese.
PM me to figure out how we can arrange these test cases. I should be back in 3 days or so.