Not sure I see anything that sticks out here. I suppose after the new program was put in (S1521), it could have been in program mode until it was power cycled? It's possible that the Run status was not noticed, as the stale data was not in an alarm state, and then when it was power cycled it was noticed, as the contacts are normally closed. I'll continue to power cycle the thing and see if I see it again.
S1503, Thu Sep 11 19:38:56 2014, Default User updated the PLC gate array
S1504, Thu Sep 11 19:39:54 2014, Default User changed mode to RUN
S1505, Thu Sep 11 21:26:54 2014, Default User changed mode to PROGRAM
S1506, Thu Sep 11 21:26:58 2014, System content changed by Default User (Program/SysConfig/Documentation)
S1507, Thu Sep 11 21:27:02 2014, Default User changed mode to RUN
S1508, Thu Sep 11 21:27:37 2014, System content changed by Default User (Program)
S1509, Thu Sep 11 21:30:06 2014, System content changed by Default User (Program)
S1510, Thu Sep 11 21:30:58 2014, System content changed by Default User (Program)
S1511, Thu Sep 11 21:31:40 2014, System content changed by Default User (Program)
S1512, Thu Sep 11 21:32:12 2014, System content changed by Default User (Program)
S1513, Thu Sep 11 21:40:35 2014, System content changed by Default User (Program/Documentation)
S1514, Thu Sep 11 21:42:21 2014, System content changed by Default User (Program/Documentation)
S1515, Thu Sep 11 21:45:03 2014, System content changed by Default User (Program/Documentation)
S1516, Thu Sep 11 21:55:21 2014, System content changed by Default User (Program/Documentation)
S1517, Thu Sep 11 22:33:25 2014, System content changed by Default User (Program/Documentation)
S1518, Thu Sep 11 22:44:41 2014, System content changed by Default User (Program/Documentation)
S1519, Sat Sep 13 01:26:10 2014, System content changed by Default User (Program)
S1520, Mon Sep 15 19:34:51 2014, System content changed by Default User (Program)
S1521, Mon Sep 15 19:46:05 2014, System content changed by Default User (Program/Documentation)
S1522, Tue Sep 16 16:20:37 2014, System was turned off
S1523, Tue Sep 16 16:20:46 2014, System was turned on
S1524, Tue Sep 16 16:20:52 2014, PLC rebooted following hardware watchdog timeout.
S1525, Tue Sep 16 16:20:52 2014, System was turned off
S1526, Tue Sep 16 16:20:52 2014, System was turned on
S1527, Tue Sep 16 16:20:57 2014, PLC rebooted following hardware watchdog timeout.
S1528, Tue Sep 16 16:20:57 2014, System was turned off
S1529, Tue Sep 16 16:20:57 2014, System was turned on
S1530, Tue Sep 16 16:21:02 2014, PLC rebooted following hardware watchdog timeout.
S1531, Tue Sep 16 16:21:02 2014, System was turned off
S1532, Tue Sep 16 16:21:02 2014, System was turned on
S1533, Tue Sep 16 16:21:07 2014, PLC rebooted following hardware watchdog timeout.
S1534, Tue Sep 16 16:21:07 2014, System was turned off
S1535, Tue Sep 16 16:21:07 2014, System was turned on
S1536, Tue Sep 16 16:21:12 2014, PLC rebooted following hardware watchdog timeout.
S1537, Tue Sep 16 16:21:12 2014, System was turned off
S1538, Tue Sep 16 16:21:12 2014, System was turned on
S1539, Tue Sep 16 16:21:17 2014, PLC rebooted following hardware watchdog timeout.
S1540, Tue Sep 16 16:21:17 2014, System was turned off
S1541, Tue Sep 16 16:21:17 2014, System was turned on
S1542, Tue Sep 16 16:21:23 2014, PLC rebooted following hardware watchdog timeout.
S1543, Tue Sep 16 16:21:23 2014, System was turned off
S1544, Tue Sep 16 16:21:23 2014, System was turned on
S1545, Tue Sep 16 16:21:28 2014, PLC rebooted following hardware watchdog timeout.
S1546, Tue Sep 16 16:21:28 2014, System was turned off
S1547, Tue Sep 16 16:21:28 2014, System was turned on
S1548, Tue Sep 16 16:21:33 2014, PLC rebooted following hardware watchdog timeout.
S1549, Tue Sep 16 16:21:33 2014, System was turned off
S1550, Tue Sep 16 16:21:33 2014, System was turned on
S1551, Tue Sep 16 16:21:38 2014, PLC rebooted following hardware watchdog timeout.
S1552, Tue Sep 16 16:21:38 2014, System was turned off
S1553, Tue Sep 16 16:21:38 2014, System was turned on
S1554, Tue Sep 16 16:49:29 2014, Default User changed mode to RUN
S1555, Tue Sep 16 16:51:12 2014, System was turned off
S1556, Tue Sep 16 16:51:30 2014, System was turned on