A migration from 1.5.3 to 1.7.1 correctly transformed the Forums options into role overrides, but the behavior is not the same than before.
If mod/forum:replypost is prevented, the "Reply" (/mod/forum/post.php?reply...) link still appears, and when clicked it shows an untranslated message: "Sorry, you cannot post in this discussion". This is very confusing for students, since now it also includes a "More information about this error" link that reinforces the idea that this is an error in the system.
I think it is even more confusing for non-english speakers, since every message in English is associated in their minds to an error (blame the Windows(TM) bluescreen!).