Hmm .. I'm sure it was something that was said at one point or other but maybe a misunderstanding ... the secure system was mystical in my early addon days and alot of the old info has stuck in my brain
Thanks .. learning something new every day.
wowpedia does have a note about buttons ( which isn't the issue henbe would have as the button hides/shows another frame )
'Protected function
I found that Frames of type Button can't call this method if the player is in combat.'
https://wowpedia.fandom.com/wiki/API_Region_Show