So, just to check, that would make the extra spacing a bug, rather than expected behaviour? (Apologies for my own lack of comprehension, here – the above post mentioning identical behaviour between Mac and Windows Scrivener has me a little confused as to whether this is considered normal or buggy.)
If it helps to elucidate, a little searching through my own forum history brings up this thread which has the issue filed as such, with an appropriate ticket number and a more helpful user than myself providing screencaps – [LH3440] Copy Special > MMD & BBCode multiplies and adds extra paragraphs between copy/pasted text - #4 by Collider – The problem seems to originate around Beta 15, but I haven’t seen any mention of it since, either in fixed or known issues, so thought it might help to flag it back up now we’re nearing release.
Again, many apologies if I’m being difficult – it’s not intentional!