I also want to change this behaviour - This is a major pain in the a** to have evernote adding spurious newlines when copy/pasting on OSX - It also seems to be inconsistent - restarting the app appears to stop the behaviour.
As has already been said - this makes evernote pretty useless for anyone who uses it to keep command line snippets. If I want a newline pasting, then i would copy it in the first place - please revert this behaviour.