Replacing Failed Drive Possible Bug?

Yesterday I replaced on of the 3TB drives in my RN312. It was in the second bay. I left the NAS powered up, removed the drive in bay 2, replaced the drive with an identical new drive and reinserted it in the NAS slot 2. Here are the log entries that show what happened during this process:

[13/10/09 17:14:23 CST] warning:disk:LOGMSG_DELETE_DISK Disk Model:WDC WD30EFRX-68EUZN0 Serial:WD-WMC4N0369713 has been removed from Channel '2' of the head unit.
[13/10/09 17:14:31 CST] warning:volume:LOGMSG_HEALTH_VOLUME Volume 'data' health changed from 'REDUNDANT' to 'DEGRADED'.
[13/10/09 17:14:33 CST] notice:disk:LOGMSG_DISK_FAIL_HALT System will be shut down in 30 minutes because of disk failure.
[13/10/09 17:16:48 CST] notice:disk:LOGMSG_ADD_DISK Disk Model:WDC WD30EFRX-68EUZN0 Serial:WD-WMC4N0512222 has been added to Channel '2' of the head unit.
[13/10/09 17:17:05 CST] notice:volume:LOGMSG_RESILVERSTARTED_VOLUME Rebuilding started for Volume 'data'.
[13/10/09 17:47:57 CST] info:system:LOGMSG_READYNASD_ABORTED_NOINFO ReadyNASOS service or process was restarted.
[13/10/09 17:47:58 CST] warning:volume:LOGMSG_HEALTH_VOLUME_WARN Volume 'data' is 'DEGRADED'.
[13/10/09 17:47:58 CST] info:system:LOGMSG_START_READYNASD ReadyNASOS background service started.
[13/10/09 17:48:13 CST] notice:volume:LOGMSG_RESILVERSTARTED_VOLUME Rebuilding started for Volume 'data'.
[13/10/10 01:00:04 CST] warning:volume:LOGMSG_HEALTH_VOLUME_WARN Volume 'data' is 'DEGRADED'.
[13/10/10 02:37:17 CST] notice:volume:LOGMSG_RESILVERCOMPLETE_VOLUME Volume 'data' has been rebuilt.
[13/10/10 02:37:19 CST] notice:volume:LOGMSG_HEALTH_VOLUME Volume 'data' health changed from 'DEGRADED' to 'REDUNDANT'.
[13/10/10 02:37:21 CST] notice:disk:LOGMSG_ZFS_DISK_STATUS_CHANGED Disk in channel '2' (Internal) changed state from RESYNC to ONLINE.

The process went fine although it took a long time. The unexpected bit of this is the warning that was given when I removed the failing drive. The system warned that the System would be shut down in 30min. I reinserted a new drive 2 min. later, the disk was recognized and the rebuild started. Then during the rebuild (30 min. later) the system shut down. This freaked me out initially, but I restarted the system and the volume rebuild continued normally until it finished successfully.

I guess the bug part could be is why did the system still shut down, even though it had a valid device in bay 2 and the rebuild had started. I would assume that if there were a drive failure and the failure state continued for 30 min, then a shutdown would occur.

Your thoughts?