[CentOS] odd mdadm behavior

Allo esteemed Centos-ers,

Noticed something funny with an mdadm mirror based raid the other day.

So I had a system disk set to mirror via mdadm.

One of the disks went south at a remote office and since there was no  
one available to swap out the disk, I thought to leave it for later.

Well, due to work being what is it, this later became a year.

During one of the servers many reboots, much of the data on the system  
went missing.  The logs even showed a gap from the day the disk went  
bad to the day this reboot occurred.

So picture a gap in the logs of about a year or so.

I first suspected foul play but soon discovered that the previous bad  
disk in the mirror became functional again and that its data basically  
put the server back to the time period being a year ago or so.

Not a big deal as I do 2 types of backups every day so recovery was  
fine.

Has any one seen this before and what could I have done to prevent this?

Thanks in advance,

- aurf