Did anything change on the forwarding table on R4 when you added the static arp entry?
Issue a ping to 172.27.0.5 from R4, and do a monitor traffic interface ge-0/0/1 on R2.
I'm curious if R2 receives an arp request from R4 for 172.27.0.5 and if R2 sends an arp reply. Take off the static arp entry before you do this.