Slitherine

I had a quick look at the manual and on the boards, but couldn't see this: do the scenarios always automatically end when all the primary objectives are captured? I had plenty of time on the clock and some secondaries to achieve but the game ended when I took the last primary.

Yes, this is the case with all current scenarios.
But an option was added recently (Morning Sun beta?) in the editor to allow players keep on after the primary objectives were met.
This means the scenarios need a slight update (just checking an option).