Saying Sheehan is 'starting to rock the boat' is being a little dramatic.
He's said the same thing throughout his short tenure as caretaker, that, in his opinion, it's best for the club to have a new manager in place before the end of the season as we're down 3 members of 1st team staff when Luke and co left, with people from U-21s coming up to help out. That's not an ideal situation to be in through to May when you're fighting for survival. It's a perfectly rational thing to say, and he's been consistent with it all along, he's not 'starting' to do anything.
Now, should he deflect those questions and say to journos that they need to speak to Montague about that side of things, that he's just thinking about taking the next game etc? Probably, yes. But let's not get too tabloid about what he's been saying.