I am having a similar problem, however legitimate messages are being deleted having a default of 5.
It seems that :
FH_DATE_PAST_20XX The date is grossly in the future.
seems to be giving high scores even though the messages are today's date.
The server's date is also correct.
Its strange because those settings have been the same for the last year of so and only in the last month or two has it started tagging legit mails as well.
OT: How would one set /reset system wide defaults for spamassasin?