Lets see if I can help.
Using the WYSIWYG editor right now and checking to see if it adds lines. Haven't seen this issue reported before.
Not sure by what you mean by spoilers staying inline? If you mean multiple spoilers on the same line then it has to be done with tables and the table needs to be set to 100% to evenly space the spoiler and each cell needs to be set to top to keep the spoilers in them at the top of the cells. And if you are copy pasting spoilers in tables it is best to do it from the source code to the source code to make sure you maintain all formatting when doing so.
If I can help further just let me know.
We added a line before the edit notification earlier tonight, I will see if that is what is causing the extra CR when editing.
This message has now been edited.
Not adding spaces here, which browser are you using?