Load stability of ADRF6750

I'm using the ADRF6750 with a 20MHz reference clock and an output frequency of 1030MHz. At 0dB attenuation, the output is within specifications and is stable UNLESS we run the output directly into a TriQuint 857216 SAW (BW=10MHz). With the SAW, the output amplitude becomes unstable. Adding 1dB of attenuation within the ADRF6750 brings back stability. The PLL lock detect remains stable in the "locked" state during these tests.

The SAW is supposed to be well matched to 50 ohms. Are there any known stability issues with the ADRF6750 output amplifier?