The only thing that makes sense is the acquiring entity tells MM, buy everything under $12.50. After the announcement undoubtedly there were large sell lots near the buyout PPS as there are a number of holders with a lower than $12.50 basis. Once those are gobbled up, the MM does both buying and selling within their own portfolios moving the PPS back and forth but just a little. Each of those trades get counted but shares are really not changing hands. MM is justified to make the market orderly, especially when there is low liquidity, which there would be after all the funds that wanted to get out, did. Looks like it is continuing today.