I can't tell what is preventing the "no pause" reward. I have it on the first few levels but not later levels. It's very hard to debug because you have to complete a level to see if the reward is given. I have now played two levels where I have very conciously not paused looking for the bug and it still is not giving the reward. I have had to stop a train and reverse it, but that didn't matter for the "no pause" reward before...
#"No Pause" reward not being given even when you don't pause
brave karma
haughty gull
Can confirm it. Got that medal in first two levels but finished all of them without using pause button (or even bringing up the menu).