The relevance of month/quarter-end trading considerations isn't limited to the US Treasury market.  Month-end for German bond markets (the largest in Europe, and the Eurozone benchmark) saw a strong rally beginning at 6:15am Eastern time.  Treasuries gleaned some benefit, but not enough to get them back into positive territory by the open.  This resulted in markedly weaker levels for 10yr yields at 8am and a 6/32nds weaker open for Fannie 3.5 MBS.

Both held almost perfectly sideways from there with the first relief coming at the 9:30am stock open.  This is a major liquidity event for markets (in that more participants come online and more money is able to be traded).  Right out of the gate, stocks were in liquidation mode with a quick 10 point sell-off in S&Ps.  Bond markets benefited immediately and in direct proportion, moving back very close to unchanged levels.

As far as bonds are concerned, nothing much has happened since then.  MBS continue to traipse along just a few ticks shy of unchanged.  Due to the timing of the gains, a few lenders have been able to offer positive reprices.  The rest of the day will be driven by the "unseen hand" as market participants make the final adjustments to their positions for the end of the quarter.  2-4pm, in particular, could be a volatile time of day because of this.