We can discuss this morning in basic terms or we can over-complicate things.  I think there are merits in both approaches.

In basic terms, stocks have been sliding with S&P futures just now turning negative on the day.  That slide has helped bonds hold ground.  It hasn't, however, helped bonds rally.  We get into the more complicated approach when we attempt to understand why.  There are two ways to do so.

1. We could conclude that stocks are still generally higher compared to Monday, and so a little bit of weakness isn't a huge deal for bonds.  You can see the relative lack of volatility in the top of the chart below.

2.  The yield curve has a say.  It arguably helped bonds rally into yesterday afternoon, but  notice 10yr yields didn't go much lower than they were at the end of last week.  The curve has gotten so low and generated so much buzz, that traders are increasingly on guard against a corrective bounce.  We can see that fear play out in the form of quick spikes higher in 10yr yields (yellow line) in both the top and bottom portions of the chart.

What does it all mean?  For now, it means that bonds have been able to delay a more pronounced move higher in yield, but to whatever extent the curve firms up, positive progress is unlikely.  A reversal toward higher stock prices would make bond gains even more unlikely.