iCloud intermittently freaks out, "has wrong magic" lines appear in log

Whilst testing iCloud integration in one of my apps, I occasionally find that changes do not propegate between devices and the log of all devices is littered with lines in the format of:

// device 1 log
Aug 14 19:18:56 unknown ubd[3585] <Warning>: Unknown error: 316: attr blob @ 0x2a7710 has wrong magic (0x00000000 != 0x41545452)
// device 2 log
Aug 14 19:19:06 unknown ubd[99] <Warning>: Unknown error: 316: attr blob @ 0x2b8240 has wrong magic (0x00000101 != 0x41545452)
// device 3 log
Aug 14 19:19:24 unknown ubd[1328] <Warning>: Unknown error: 316: attr blob @ 0xed7c0b0 has wrong magic (0xc0ed7bdb != 0x41545452)

It seems that ubd is the Ubiquity daemon which powers iCloud and presumably the blob is related to the document I'm trying to sync, but magic?

To be clear, iCloud syncing in this app typically does work (and DropBox sync is rock solid). This problem is just an occasional phase. I haven't quite nailed down what causes it to occur or disappear yet.

The question, in short, is: what is this magic, is it important that it is 'wrong' and has anyone else had experience with this issue?