In "New wikitext mode", if the cursor is on the last line of a paragraph, and there is a blank line below and then another paragraph: if I press the down key, instead of moving the cursor to the blank line, it moves to first line of the next paragraph. That is, it skips the blank line.
This is so annoying I've disabled New wikitext mode. There should be an option to disable this "feature".
Tested in Chrome version 74.0.3729.169 (Official Build) (64-bit) at the English Wikipedia.