And the headline says merger. This was obviously a merger that was effected through a transaction that took the form of an acquistion. This is true of many mergers. It is rare these days to see a combination transaction that formally qualifies as a true merger: a transaction structured to result in a brand new company the stock of which is given to the shareholders of both merging companies.
The M&A world sees the transaction between Nationstar and WMIH as a merger because it was a friendly combination transaction that was agreed to by both companies' boards, regardless of how it was structured. The substance is more important than the form.
See project Eclipse, which is also the reason for the drop in Coopers pps because of shares that yet have to be authorized io to complete the acquisition.