What causes the Spacebar to move the caret instead of starting playback?

I often press something that triggers this behaviour, yet I don’t know what it is.

Can someone explain it to me?

If you are in write mode but are not entering notes (no caret visible) then you will get playback.
If you press shift-N (or press the return/enter key) you will then start entering (invisible) rests unless you press A to G for note entry. So what the caret movement is displaying is where the note will be entered (Dorico fills up the gaps before with appropriate rests).

Ok, so I basically just need to press enter or shift-N again, the caret will fade and the space bar will trigger playback.
I tested it here and it worked, thanks.