Webproxy on pppoe connections does not work- Help!!!!

Hi,
we have setup the webproxy according to all of the doco.
It is on port 8080 and we have dst-nat rule to redirect anything from the client network on port 80 to 8080.the webproxy is on port 8080 and src-address 0.0.0.0.

From a standard client that gets a dhcp address from the mikrotik box they browse the web fine. i see the dst-nat rule showing packets flowing and the webproxy stats counting up.

However from a client that is a pppoe user, any browsing does not work. I see the dst-nat packets counting up when they go to browse a webpage but the webproxy stats do not climb and the client eventually times out.
i have checked mtu’s etc and they are all set correctly.
I have tried setting the proxy manually in internet explorer of the pppoe client and that also works fine.
i can telent from the pppoe client to the webproxy 8080 and get a response so that says comms is working fine.
Its just it wont work as a transparent proxy for pppoe users.

Anyone got any ideas im really lost on this one.

Got it fixed.
Did a system reset config, restored my backup.
could browse via proxy from a pppoe user plugged direct into the RB, but not from a downchain router aka CPE router. Changed MRU to 1480 was 1492 and all ok now for all types of users