I think this paragraph on Al-Akhbar explains why Maliki started to improve his relation with the Sadrists a week ago []:
Sources said that the cause of the armed confrontations occurred between Al-Sadr and the government forces in Basra and Sadr-City last year, is the U.S. reports indicated significant progress of the Sadr movement will affect the results of the Provincial elections. The American advised the Iraqi government to act against the growing popularity of the Sadrists.
Since the American grip on the Iraqi decision making is not as hard as it used to be before, not only Maliki and his Dawa Party, Al-Watan
A delegation representing the tribes of the mid-Euphrates and the western region also political parties, including the Iraqi Islamic Party, Dawa party and the Supreme Council met with the political body of Sadrists.
And the Sadrists are “spoiled” with these “offers”, so the needed a special meeting to pick a parties and political blocs to support:
Various Sadrists bodies of media, political, social movement, the leaders of Al-Momahidon and Sadrists members in the Parliament in the joint meeting formed a joint meeting, to discuss developments of the Sadrists position from the coming Provincial election, including strengthen the presence of Sadr Trend to win seats in the elections by supporting independent candidates or contribute in supporting specific electoral lists.