Yes, I checked SEL logs. There no helpful info except "Physical Scrty" warning when value changes to 0x0010:
| 206 | 09/02/2013 06:57:02 | Physical Scrty | Physical Security (Chassis Intrusion) | reports LAN Leash has been lost - Asserted |
Unfortunately I can't find the alert when value changes back to 0x0000. :-(