A late reply, but hey:
Unfortunately you didn't show the relevant parts, for example, which units your fdisk output shows (sectors? cylinders?)
Nonetheless it looks like you got bitten by the bug of the 0.90 meta data block:
0, 0.90
Use the original 0.90 format superblock. This format limits arrays to 28 component devices and limits component devices of levels 1 and greater to 2 terabytes. It is also possible for there to be confusion about whether the superblock applies to a whole device or just the last partition, if that partition starts on a 64K boundary.
That means if you have a 0.90 meta data block on the last partition, and it starts on a 64k boundary, mdadm will assume the whole disk belongs to the raid. What you're seeing is the partition table of /dev/sda within the RAID. Of course this will give you massive corruption if you try to access anything within that RAID.
Upgrade ASAP (I can speak out of experience).