This is a little hard. Basically when on maternity leave your job is someone elses. Remember that we aren't even guaranteed to get our "own" job back when we return, just one of equal standing. Your situation is a little odd with you working whilst on leave so it's hard to comment on. I personally am going to completely turn off to what's going on whilst I'm off and am prepared to go back to whatever the situation is when the time comes. I just hope my replacement lasts as I have a complex position that has a history of people walking out of it. I will visit the office only to show bubs around the place. I think you need to try to just shut off work until you go back.