Guan,
Yes, one of the newer cyclics in 9.0 (k1?), and from the beginning in 10.0, introduced one new message type in particular, 1051, and that is probably responsible for the big jump in message volume. I think almost everyone is suppressing this one, at least.
I agree it is less than perfect to not be able to see which pernr is responsible for the message. I'd like to see this come up in a future update. However, I expect you can see the same message (unless suppressed) in the payroll log back in SAP, and there it would be associated with the pernr. I don't spend a lot of time myself in the payroll transactions, so perhaps someone else can weigh in on this?