Whoops - hit the wrong button. Sorry. I'll start again. I was messing around trying to get an image included, and made a mistake...
I just tried this (oscDiff) using both the latest subversion of IC5141 (5.10.41.500.1.18) together with spectre from MMSIM60 USR1 - and then I also tried using the Base CD version of IC5141 - with spectre from the same version.
I tried with and without highorder=yes in case that made any difference (it didn't to the phase noise results).
I got consistent results as the picture shows:
The blue line shows the traditional phase noise plot - and the yellow line (which is almost identical except at higher frequencies) as you can see. The am noise (the red line) is a fair way down compared with the pm/phase noise - exactly as you'd expect. Note, I'm plotting the am and pm noise in dBc for comparison.
So, what version were you using - the above looks reasonable to me, and not like what you described.
Regards,
Andrew.