I cannot think of anything else. If you don’t get a suitable response here on the forum, may I suggest sending a report to Mikrotik with a description of the challenge. This is how: http://www.mikrotik.com/testdocs/ros/2.9/system/support.php
@surfertim, Thanks a million for your support. Turns out that the problem was in mangle.
When connecting to orange using the RB411U/Huawei E156G one rule was automatically added in mangle. The rule is changing the MSS for all outbound TCP traffic. The mistake - or the problem is that no rule was added for the inbound traffic. When adding the same rule for the inbound traffic everything works fine.
Credit to my friend from CZ for solving this problem. That was a real tough one.
I have exactly the same problem with you
the problem is not the setting but the modem firmware mikrotik
I have been able to fix the problem, the modem firmware upgrade
