One of the last legal dramas from the subprime crisis took a surprise turn last week when FHFA sued Wells over a case that had been settled earlier this year. At stake: more than $1 billion in RMBS issued 13 years ago.

Fannie's MBS issuance was up significantly from April to May while Freddie posted a smaller monthly gain. Purchase mortgages and refinancing both rose substantially.

The FHFA has postponed implementation of a complex data standardization process as trade groups worry whether the industry is ready.