Is This Really How It's Going To End?! - S5-E15
Continuity mistake: When Dan hands Ella the phone number, he's holding it by pinching it on the bottom. In the next shot, he's holding it on the side.
A Chance At a Happy Ending - S5-E16
Continuity mistake: A guy with a face tattoo is in the opening scene, then the tattoo isn't there when the guard gets up.
Answer: Boo Normal and Once Upon a Time were going to be part of season 4, then the show got cancelled (before being picked up elsewhere). As such they were added on to the end of season three as "bonus" episodes, hence the continuity being off. But not really a mistake, just a quirk of broadcasting. Boo Normal was originally going to be between the episodes "High School Poppycock" and "Infernal Guinea Pig" in season 3 before being slated for season 4, presumably because aside from the point you've raised, it was fairly flexible, continuity-wise.
Jon Sandys ★