I have wiresharks gathered on MS350 switches running MS12.27 that show this is not true.  MCAST will continue from the initial address and cause the port to send out both streams until the first stream times out.   This is consistent with Fast-Leave / Immediate-Leave not being enabled or correctly implemented.   In a Crestron NVX system you can turn the stream bandwidth down from 950Mbps to 450Mbps to get around this limitation assuming you are happy with the reduced video quality. ... View more