Since a few days (and I'm positive it started shortly before I updated my server from 13.04->13.10) my mdadm is resyncing on every boot. In the syslog, I get the following output

[    0.809256] md: linear personality registered for level -1
[    0.811412] md: multipath personality registered for level -4
[    0.813153] md: raid0 personality registered for level 0
[    0.815201] md: raid1 personality registered for level 1
[    1.101517] md: raid6 personality registered for level 6
[    1.101520] md: raid5 personality registered for level 5
[    1.101522] md: raid4 personality registered for level 4
[    1.106825] md: raid10 personality registered for level 10
[    1.935882] md: bind<sdc1>
[    1.943367] md: bind<sdb1>
[    1.945199] md/raid1:md0: not clean -- starting background reconstruction
[    1.945204] md/raid1:md0: active with 2 out of 2 mirrors
[    1.945225] md0: detected capacity change from 0 to 2000396680192
[    1.945351] md: resync of RAID array md0
[    1.945357] md: minimum _guaranteed_  speed: 1000 KB/sec/disk.
[    1.945359] md: using maximum available idle IO bandwidth (but not more than 200000 KB/sec) for resync.
[    1.945362] md: using 128k window, over a total of 1953512383k.
[    2.220468]  md0: unknown partition table

I'm not sure what's up with that detected capacity change, looking at some old logs, this does have appeared earlier as well without a resync right afterwards. In fact, I let it run yesterday until completion and rebooted, and then it wouldn't resync, but today it does resync again. For instance, yesterday I got:

[    1.872123] md: bind<sdc1>
[    1.950946] md: bind<sdb1>
[    1.952782] md/raid1:md0: active with 2 out of 2 mirrors
[    1.952807] md0: detected capacity change from 0 to 2000396680192
[    1.954598]  md0: unknown partition table

So it seems to be a problem that the RAID array does not get marked as clean after every shutdown? How can I troubleshoot this? The disks themselves are both fine, SMART tells me no errors, everything ok.