It was a pretty simple day as far as bond markets are concerned.  The collective unconscious of the bond-trading population was perfectly content to extent the weekend, unofficially.  For most of the day, it looked like a perfectly viable plan, considering a relative absence of movement in Treasuries and MBS.  But plans were foiled in the late afternoon by corporate bond issuance.

Particularly, Shire off-loaded $12.1 bln in 3, 5, 7, and 10yr notes.  For perspective, anything over $10bln would be considered a "heavy day" of CUMULATIVE corporate bond issuance (i.e. from multiple sellers).  When it's coming from just one deal, the moral of the story is that it's a very big deal.  

Only a few corporate deals per year go over $10bln, so when one of them hits on a sleepy monday, bonds feel it.  This was the exclusive and incontrovertible source of this afternoon's bond market weakness.  Even then, it left 10yr yields a mere 1.3bps higher on the day and Fannie 3.0 MBS just over an eighth of a point lower.  Both also remain well within last week's new, weaker range as they continue grinding toward this Wednesday's central bank announcements (Bank of Japan and the Fed).