Maybe this has something to do with it . . . some sort of mixing of spending streams? At this point (and until about three weeks ago) it didn't seem that the DNC or any other mainstream outlet took Sanders seriously, so it wouldn't occur to them to worry about the DNC's agreement with anyone else.
From Politico in August.
http://www.politico.com/story/2015/08/dnc-democratic-committee-hillary-clinton-fundraising-agreement-2016-121813
The document will enable the DNC and the campaign to conduct events and other fundraising activities together that will generate money for both entities. Clinton wouldnt have access to the money unless and until shes the nominee but this is seen as an essential step for banking cash to counter whats expected to be massive Republican spending next year.
. . . All 50 state parties were invited to join the agreement as well. Several had already pursued their own joint fundraising agreements with the Clinton campaign while the DNC had held off on signing largely over disagreements over how the money would be able to be spent. The Clinton campaign, wary of management and structural problems at the DNC, insisted on a tight rein on spending.
. . . A DNC official said the money would build infrastructure to to support whoever the eventual Democratic nominee is as soon as there is a nominee. It will help the party make critical investments in technology, in voter outreach and in helping get out our message leading up to the general election in 2016.
. . . The DNC says its pursuing similar agreements with the other Democratic primary campaigns, but so far, those havent materialized.