Sirrian had a post on the 1.0.7 Patch Preview 2 blog post:
In version 1.0.5 and earlier, all gem drops were totally random… the AI and the human both had an equal chance of lucky drops – cases where gems drop in to set up or activate good skull matches or 4-of-a-kind matches.
Unfortunately, a lot of players felt that the AI was cheating (for the record it definitely wasn’t). It’s an unfortunate way that our brains are wired so that negative events are remembered more clearly than positive ones – it’s called “recall bias”.
We implemented a “combo-breaker”, something that detected if the AI player was about to get a lucky drop, and if you (as a human player) hadn’t had a bunch of luck yourself, then it altered the gems dropping in to disadvantage the AI player.
The complaints have mostly stopped since then, but we know some players enjoy the tension of a more-evenly-matched contest, so we’ve disabled the combo-breaker in all difficulties above normal in 1.0.7.