Q: Mysterious line breaks in Mail

Technically, this is a Yosemite question, but I don't seem to be able to select that as a Communities option.

Every since upgrading to Yosemite, Mail has exhibited the strangest behavior around smart characters -- apostrophes, smart quotes, ellipses, en dashes, etc. Mail converts the character and automatically inserts a line break. Totally messes me up. I thought I was hittng a bad key combination, but then I noticed the pattern with smart characters. An example of how an email would look.

Here’

s what happens when I type a smart quote (the apostrophe above) and don’

t intend to hit return. It’

s a soft return.

It also happens in other cases, like when I insert a quotation. “I wonder what will happen,”

I think to myself, “when mac converts my standard quotes to smart quotes.”

See what I mean? I didn’

t mean to start a new line after that…

or after that ellipsis. In fact, it happens any time mac senses a fun new punctuation —

like, say, an en-dash —

and just automatically puts in a carriage return. What gives? “What gives,”

I say.

 

Where did the mysterious line break come from? More important -- HOW DO I MAKE IT STOP?