Multiple "Returns" Not Creating Space

[Essayoh]

Pressing "Return" once after a line of text creates a full line break as expected. Pressing "Return" twice creates appropriate space in the Editor but in Preview and upon Publish in fact creates a single-space line break, much more narrow vertically, than the single-press of Return. Here's an animated GIF of this behavior in action:

https://cloudup.com/cGofGbBnspN

To reproduce: 1.) Create new Post 2.) Type some text, press Return one time. 3.) Type some more text, press Return two times. 4.) Type some test, Preview Post.