Post-Destroyed Gems Matching Up but Not Matching

So I've only seen this once (so far) while running through Story/QB matches with Chandra, and given the number of ways I'm blowing up chunks of the board (first PW ability, Volcanic Rumbler, Volcanic Eruption, Sword of the Animist), I'm not sure what exactly triggered the destruction of the board in this instance. Anyway, whatever it was, I blew up a 3x3 hole, which caused a minor cascade, and at the end of it, 3 black gems dropped in a row to fill in the bottom row of the 3x3 gap, and they didn't automatically match up. I still had a match to make (either from a match-5 or because this happened after I used her first PW ability, not sure which now), and I was able to move the middle black gem up to fill a hole in a match-4, but until I did that, I was looking at 3 black gems in a row. Wishing I'd taken a screenshot of it now, but thought of that too late .