From a recent alert on the MBS Dashboard: "Late day illiquidity and a stock market rally are weighing on MBS this afternoon. Prices are in line with their lows of the day and while the reprice scene has been fairly quiet today, it's not out of the realm of possibility for a lender or two to take some rebate off the table heading into the weekend. Fannie 3.5's are down 12 ticks on the day at 100-22 and 4.0's are down 8 ticks at 103-03"

Since that alert, MBS have gained back a few ticks, making things look slightly less dire, though reprice risk remains.

Treasuries were also able to hold below their high yields of the day into the late stock market push:

Perhaps the scariest prospect is what will happen to Treasuries if the following breakout of the trend channel in S&P's is confirmed next week.  Today is their highest close in more than 2 months and a definitely "test" of trend channel breakout: