Well that showed up an issue.
First time around I didn't realise that I needed to place the cursor between the 2 square bracketed spoiler thingumyjigs. When I went back and edited it then had 2 spoiler tabs, so I clicked edit again to remove the extra unwanted one, couldn't see how to change it so clicked cancel, and low and behold, now another spoiler tab had appeared.
It would seem that every time you click on edit, even when you don't click save (& this I find most peculiar) it adds another blank spoiler.
How is it even adding them if I'm not saving any changes?
Just noticed that it's only the last additional spoiler which has no content, all the others are duplication of the original content.