Incremental rebuild of AssetBundles always rebuilds one AB

Hello,

I've stumbled upon a weird issue - one of our AssetBundles (out of 5 in total) always gets rebuild, even though no file changes (by looking at VCS status to look at the changes); when comparing the manifests, diff shows difference only in the CRC and hash lines.

What exactly is the mechanism to determine whether or not the AB needs to be rebuilt? This would (hopefully) allow us to track down the issue.