Word Joiner displays incorrectly in iBooks Mac

I have an epub created by Scrivener which displays correctly on every epub reader software I have except iBooks.

The character in question is a Word Joiner (zero width non-breaking space), but even worse, it's not consistent. In the following text,

“When he allowed them to leave—at three-fifteen—he had”

Excerpt From: Tony Lavely. “Discoveries.” iBooks.

(Firefox displays the text correctly.) However, iBooks does not:

The sequence of characters for the first em dash is "e WordJoiner emdash a" (without the spaces) and for the second em dash, it's "n WordJoiner emdash h"

Does anyone have an idea what I might have done incorrectly? It happens more than once in this file, but infrequently. From a reader's POV, however, once is too many times.

Thanks for help!

tony