Timing of FUD to AD9858

Suppose I have the following parameters:

FTW = 100MHz

DFTW = 10MHz

DFRRW = 1ms

And I am strobing FUD every 5ms.

I would expect to see a sawtooth chirp with outputs at 100, 110, 120, 130 and 140MHz.  However, after the first sweep, I see a bunch of sweeps at 110, 120, 130, 140 and 150MHz.  In other words, the sweep begins at the second tone, and gives me an extra tone at the end.  This seems to occur when the sweep time is an integer multiple of the DFRRW time.  If I change my FUD so that it arrives 8ns earlier or later, the device seems to operate properly.  From the outside looking in, there seems to be a race condition when FUD is strobed at the same time as the frequency accumulator is getting updated.

Is this a known issue with this device?

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