Thanks so much for responding. I was getting worried that no-one had seen this question
I have indeed got "link to next activity" set. If I turn it off, I am left with only one link, the "Return to ..." link. It is still a link, and doesn't turn into a button if I remove the "link to next activity". Also, removing that setting means the student doesn't have the link to the next thing they have to do which is what I need there.
I am actually on MoodleCloud 3.4 now - upgraded today. Unfortunately the new navigation is much too invasive. I need to turn it off (hence my newest question) and the students shouldn't be jumping around the place. But that's a different question.
But, to address this particular problem, I think it must be a bug that there is no space between the two links? What do you think? Alternatively, if they were meant to be shown as buttons, and that CSS has gone missing somehow, then perhaps that is the problem, and the missing space wouldn't then matter? Can you say what it is *meant* to look like? Were the buttons shown in the older documentation deliberately removed? Is it *meant* to look like links now?