Perhaps it is in using 'quote' rather than 'reply' exclusively. Following your example if using 'reply' it works fine for me for three different posts above. However when I use 'quote' all it says is "message moved to multi-quote" - pushed again it says "message removed from multi-quote" (so I'm in the dark about how to use that function - so I never use it

).
In saying that, and may be this is the issue, if highlighting text in a post (like in yours above) that has already been quoted by the posters (e.g. when you added from lainey as a reply "
If you click "reply" on the quote you want to reply to it will add the quote once. I hope this helps.") it does what you say and adds the original quote twice, and in my example it does not add the one from lainey. I've never figured this muti quote thing out - to add both quotes in a post from someone else along with the posters quote simultaneously without just copying the first part and then quoting it.
I know how to change a spark plug though, really.