Table saw misbehavior?

I have a Grizzly contractor table saw that usually works very well.  Today, I encountered a problem and cannot figure out the cause.  I was trying to crosscut a miter in walnut that is 1/4 x 2.5 inches.  I was using a Dewalt 50 tooth combination blade.  I made a test cut in 3/4 inch pine scrap that was also 2.5 inches wide and the result was good.  The cut was square to the side, and the 2 pieces joined nicely at 90 degrees.

 I lowered the blade so that only 3 teeth would protrude above the surface of the walnut and made a cut.  Oops!  The cut in walnut was NOT square to the side.  The cut starts out square, but it appears as if the blade is bending a little half-way thru the cut which causes the blade to veer to the left.  I hold the piece tightly against the fence.

 I ran the pine thru again without changing the blade height, and the same thing happened.  This time, of course, I did not cut all the way thru the thickness of the board.  There was a lot of wood on either side and above the blade throughout the cut.

So, could I have a fence problem?  The blade has some resin build-up; could that be it?