Intention: To create a block of text to check line wrapping.
Expectation: That I'd end up with a block of plain paragraph-formatted text.
Steps to reproduce:
1) Start with a page containing some text and a few section headings. In my case, it was a list.
2) Select all the text in one section using arrow/cursor keys, including all of the last line (including the blank part at the end of the paragraph), but none of the section heading that follows.
4) Copy this.
5) Make a new, blank paragraph-formatted line.
6) Paste the copied text into the new line.
Results: You get the desired paragraph, followed by a == <nowiki /> == section heading.
(For bonus points, if you skip step #5, you'll get your pasted text set to ==Section heading== formatting.)