I just noticed that if I get a specific activity (a page) in a non-active world, I only get the new activity sound and not the sound I specified for the specific event. As far as I recall, I used to get the sound for the specific event (or possibly both, can't quite recall).
And yes, 'Only if inactive' is unchecked.
I think you will find that if Windows is asked to play two sounds in quick succession that the first is terminated and then the second started.
A work-around would be to use a "catch-all" trigger (*) with a high sequence number, that does nothing but play your inactivity sound (marked "if inactive" of course) so that you either get the page or the new activity sound but not both.
What I find odd is that I am pretty sure I used to get both, or possibly just the event-sound, but not I only get the new activity sound.
I don't imagine it would be possible to add a setting that allows the event-sound to override the new activity sound?
I just tested and found the specific sound (the trigger) is the one that I heard. However if the trigger didn't match I got the new activity sound.