Non-breaking hyphens

I just had a response from a critiquer which indicated that all of the non-breaking hyphens in the MS Word file that I sent her vanished somewhere along the line. Which means that a sentence like "I didn't know -- couldn't have known -- that the still-smoking gun was in my hand" would turn into the nonsensical "I didn't know couldn't have known that the stillsmoking gun was in my hand".

I search and replace all my hyphens to non-breaking hyphens when I prepare a manuscript for submission, so that hyphenated words and em-dashes don't break across lines. This is appropriate for paper submissions. But this isn't the first time those non-breaking hyphens have failed to appear in an electronic submission. I think I'm going to stop doing that.