17 to 9.  That's the current score between Treasuries and MBS in terms of day-over-day price gains.  Or look at it this way.  10yr yields just had their lowest 3pm close of the year at 2.426 vs 2.438 previously.  MBS, on the other hand, are heading out at 102-20 vs a previous high close of 103-08.  MBS have been bumping their heads on July's best levels while Treasuries are convincingly through theirs.

The most obvious reason for the underperformance is that the overall bond market rally is driven by geopolitics and European weakness--two things that have a much more direct effect on Treasuries vs MBS.  All that to say: yes, there was a pretty substantial rally today, and this is why MBS didn't get to participate as much.

To recap the actual events:

• weak economic data in Europe overnight
• technical buying in European bonds, selling in European stocks bred same in US markets
• snowball buying in European bonds during US hours bred same in US markets
• newswires saying Ukrainian fighter jet shot down on Eastern border fueled further flight-to-safety, further snow-ball buying just before noon.
• (note: "snowball buying" generally means that buying is happening because of the buying that immediately preceded it.  For instance, if I am bet on 10yr yields moving higher from 2.47, and if I set an automatic line in the sand to cover that bet if rates fall to 2.44, and someone else does the same but sets their line in the sand at 2.43, as soon as rates hit my 2.44 'stop,' I'm forced to buy, further dropping rates and increasing the odds that the next guy in line is "stopped-out" as well.  And so on...)

The rally never really let up, largely because of this snowball phenomenon.