Hello,
I’ve had this in my v6.47.9 (hAP lite) config export:
/ppp profile add change-tcp-mss=yes idle-timeout=1m name=def-enc-ondemand use-encryption=yes
/interface l2tp-client add allow-fast-path=yes connect-to=[server] dial-on-demand=yes disabled=no ipsec-secret=[secret] keepalive-timeout=disabled name=l2tp-ondemand password=[password] profile=def-enc-ondemand use-ipsec=yes user=[user]
which it managed to import (from text export, line by line being individually pasted), with no errors, into 7.12.1 (on an RB3011)
But it did not want to correctly work - the client connection went on to establish immediately after enabling it, and went on to re-establish itself every minute, did not ever go idle, ‘waiting for packets’ for long enough to notice. ppp debug log did show it go ‘inactive’ and disconnecting, then immediately reactivating itself.
I have replicated by hand other paraphernalia, like ensuring no ND is sent (or listened) off this interface, and then a little more restrictive rule for NAT over the interface - but it did not help.
(edit, i also did not reboot the 3011 after import 
)
Eventually, after checking/changing every option that made sense to touch (idle timeout, bridge learning, allow fast path) and returning it back to original state in winbox, it started working as it should, with this outcome in export:
/ppp profile add change-tcp-mss=yes idle-timeout=1m name=def-enc-ondemand use-encryption=yes
/interface l2tp-client add allow-fast-path=yes connect-to=[server] dial-on-demand=yes disabled=no ipsec-secret=[secret] keepalive-timeout=disabled name=l2tp-ondemand password=[password] profile=def-enc-ondemand use-ipsec=yes user=[user]
(yes it is identical to what exported off v6… )
Did anybody encounter something like this with v7 replicating the v6 config, in particular on l2tp/ipsec connection with dial-on-demand?
Hopefully the above makes sense…?