Mighty blow & tremendous blow hit messages are skipped
When you use the powerful barbarian blows, you don't see the message what happened. The hit/miss message is populated so that it's instantly skipped and the first message you see is the next thing that happens - usually what the monster does. If you manage to kill something with the blow, no message is visible. You need to navigate to the message log to see it.
Not sure if this is the case with other actions also activated via the class powers.