From what I have been able to tell, it's a programmed maximum of 139 rows in the database table, at least on 5.8 FP6 which is what we are on. I'm not sure how changable this is.
Do you have a 6110 as well, or just 6160? I'm pretty sure Prairiefyre wouldn't include full logging/reporting capabilities in the 6160 given that is the role of their 6110.