I bought up all the market sells on poli yesterday up to 1btc worth and when the screen refreshed there were already 10 sell orders automatically created to exactly the same low price. Whoever runs these bots has A) Deep pockets and B) lots of VNL.
However one thing is for sure, they can't have unlimited of both  .

Also, if I did market buys at trex it would have taken price up to ~19k which means supression was heavier at poli (only got to 14k). But this is not always the case, so please 'shop around' the two exchanges before buying and buy the cheaper of the two to get best value and take out the bots.