iSCSI Initiator using Round Robin w/ Subset dropping paths into Standby on its own?

Using the MS iSCSI Initiator on a Windows 2008 R2 host to connect to iSCSI target on an IBM XIV.  When discovered, the targets on the XIV report that they are available via six paths.  We want to use only four, so we've configured our initiator to use "Round Robin with Subset" and explicitly set the two undesired paths to standby mode rather than active.

Over time, we noticed an issue where all of this host'ss iSCSI traffic was being sent over only one of the paths rather than balanced among the four we'd explicitly selected.  Upon reviewing our Round Robin with Subset settings for the particular target, only one of the paths was set to Active with the remaining paths set to Standby.

Is this expected?  Will the MS iSCSI stack periodically modify the path preferences we manually set?  If so, what's the trigger and logic behind it?  Is there a better algorithm we should be using to tell the initiator to only use the paths we want?

Thanks!

Ray