In the new composer, type something, press return, (which inserts a double-line paragraph break 
) and then type something else. Now, select everything you’ve written, click the ⊕ button, and select Blur Spoiler.
Expected: Spoiler-blurred text
Actual: The second paragraph is deleted 
and the first paragraph has the text [spoiler] prepended to it, like this:
[spoiler]First para