L2TP SRC ADDRESS ISSUE

Here is my topology:

R1(l2tp-client) ----> internet -----> R2(l2tp-server)

R1 pri ip:211.1.1.1 /24
R1 tunnel ip 1.1.1.1

R2 ip: 37.5.5.5/24
R2 sec ip: 4.4.4.4/24
R2 tunnel ip 1.1.1.2

I want to pass dest prefix 172.16.0.0/24 traffic which is originating from R2 through tunnel to R1

Here is mangle from R2:
add action=mark-routing chain=output dst-address=172.16.0.0/24 new-routing-mark=global passthrough=no

and route from the same router:
add distance=1 gateway=1.1.1.1 routing-mark=global


on R1 in L2tp interface torch I see: icmp coming from 37.5.5.5

then I tried to set " add distance=1 gateway=1.1.1.1 routing-mark=global " with preferred source of 4.4.4.4 on R2 but I still see
primary ip(37.5.5.5) in torch as a source from R2
and manual says:
" prf-src parameter: Which of the local IP addresses to use for locally originated packets that are sent via this route. "


Question: why is setting preferred source does not change packet source address originating from that router?

Did I misunderstand manual or there is another issue with soft?