Twitter Censoring Bird Flu Tweets, Why?

Anyone have any idea why Twitter is censoring these tweets about the Federal Government soliciting for  .6 Billion dollar emergency Human clinical trials of Adjuvent Bird Flu vaccines, and post viral infection, 24 hour advanced notice, emergency Human treatment trials?


Update 5/4/13:

 Looks like the tweet with the #FedBizOpps hashtag is now appearing 48 hours after the fact. Certainty a strange way for a site like Twitter to function; bury a tweet two days back in the timeline,  seems contrary to the Twitter's advertised fundamental premise.