True BCVs (mirrors of devices using mirror positions) have never existed in VMAX.  When you use symmir commands on VMAX, they are being translated into clone commands.  When you perform an "establish" it starts a clone activate with pre-copy.  Precopy is a background operation that looks for tracks to copy that have been changed on the source.  The device will show "established" once the precopy has completed one pass.  It will continue to loop on the device until you "split", which is a clone activate.  As long as there are writes to the source device, there will always be tracks that haven't copied yet.  I would highly recommend you switch to native clone commands, it will lessen the confusion.  There is always something lost in translation.
[IMAGE] Notice that SLV 0386->04B0  The Inv. Tracks decreases from the start of query as compare to the subsequent query.
Vmax BCV 3 thin source devices to 3 bcv devices. During the copy process, one 
of the devices pair's rather than decreases, it increases