No matter how often or when I run the same subrange repair, it ALWAYS tells me that some ranges are our of sync. Tested in 3.9 + 3.10 (git trunk of 2016-08-17). The cluster is sane. All nodes are up, cluster is not overloaded.
I guess this is not a desired behaviour. I'd expect that a repair does what it says and a consecutive repair shouldn't report "out of syncs" any more if the cluster is sane.
Especially for tables with MVs that puts a lot of pressure during repair as ranges are repaired over and over again.
See traces of different runs attached.