RTG ports could be "simple ports" like ge-0/0/0 or it could be also aggregated ingerfaces (ae0) with family ethernet-switching Primary and backup need not to be of same type. By setting aggregated interfaces "set interfaces ae0 aggregated-ethernet-options minimum-links X" you could specify when is aggregated interface treated like not working.
Go to configuration mode
cisco >configure terminal "Switch(conf)#
Juniper >configure "user@switch#"
disable spanning tree on port
Spanning tree is turned off automatically on flex links
user@host# set protocols rstp interfaces ge-0/0/5 disable
user@host# set protocols rstp interfaces ge-0/0/6 disable