SL360 - Audio resuming when navigating backwards through layers?

Strange one this. Sorry if the explanation is poor, it's difficult to label up 'slides' + 'layers'.

I've got a couple of slides set up to use layers to reduce the overall slide count. 

I've got manual Next/Previous buttons, and triggers set up to stop audio if they're clicked, so the layer voiceovers don't clash.

If I go 1 > 2 > 3, everything plays as expected. If I toggle between 2 and 3, everything is fine.

If I go 2 > 1, then back to 2, it seems as though the slide 2 audio resumes from where it was left off (unless it was allowed to complete, in which case it starts from the beginning as expected).

All slides and layers are set to reset to initial state.

I've attached a simplified version.  Same thing happens on a slide + single layer setup.

Navigate back/forth as soon as the next and previous arrows appear, rather than waiting for the voice over to complete playing.  When you get back to the first additional layer, the voiceover doesn't go back to the start.

For comparison, try again once the playback completes on the first additional layer.

Just wondering if there's a bug or something I've done wrong?