I first read about this problem being reported (in forums at least) in version 6.0.9. Evernote acknowledged it then, and at points beyond. There have been a few releases since then, but it seems to persist.
Same for me too on OS 10.10.4. and EN 6.0.16. Seems to get worse as the note gets longer. Simple text. Occasional bulleted and number list. Occasional bolding/underlining. No images or any other elements. Would be really nice to have this fixed. I've been following the conversation since 6.0.9. And as many have said, it renders EN practically unusable.