Andes 2 - Strange optimized results

I am using Ansoft's designer 2 to optimize a oscillator design. I am optimizing phase noise at 1k & 10k. Now the optimizer improves the PN figures from my design values. When I re-run the non linear simulation with these updated optimized values, the PN degrades by about 4dB? Running the optimizer again, improves the PN by 4dB without changing it's previous optimized values. The optimizer is set to update design values automatically. I also tried it with the various optimizer algorithms, same result. Any ideas?

Thanks, E