I was playing normally (species mode, if that's important) and, I was just starting, with a few pieces placed in each pilar, (like, 4 or 6) and the game, just decide to end. It ended normally like when you finish all the pilars, with the score and the prize tiles, but just before filling all the tiles. I dind't hit the "end game button" and it's not the first time it happened, before I just assumed that I've got full pilars and wans't paying attention or something, this time, I'm pretty 100% sure.

This is happening to me as well. I finished one pilar complete with 12 tiles and then the other two I still had 6 tiles each to place but the game ended on me.

I suspect it's ending when there are no viable moves even though we have shuffles left? Just a guess though; doesn't happen too often. [edit] Almost positive now. If you make sure to keep a column at 11/12 instead of filling it, or keep a wildcard at the top of a column before shuffling you can be sure it won't end the game early on you.