As documented at CONF-6992 there are various Confluence bugs about switching between Rich Text Editor and Wiki Markup Editor. For the most part all these bugs can be tested by setting the wiki markup in the wiki markup editor, switching to the RTE tab, and switching back again.

There are some cases though, such as CONF-14512 where that use case round-trips correctly, but saving the page in between causes a change.

It seems that somewhere in the process of saving and retrieving the page, newline characters can get converted to carriage-return plus newline character pairs, and that there are instances where the Renderer treats these differently.