Harmonic balance not matching transient with harm_tuner

I have been experimenting with the new load pull functionality using the harm_tuner component, and am quite confused about some results. I am seeing dramatically different results from the hb sim vs when I do a transient simulation with the tuner in place to sanity check, or similarly check the tstab waveforms. Harmonic balance shows several orders of magnitude larger power than I see in transient.

In an effort to debug this in a simpler setup I made the following testbench, which shows somewhat similar behavior. The idea is that the tuners convert from 50 Ohms to some lower impedance, but are matched to each-other so all input power should show up at the output.

Both ports are 50 Ohms. Port1 is driving a 10 GHz 0 dBm tone.

The source/load tuners are configured identically:

A sp sim shows s11=s22=0 (linear), and s12=s21=1 (also linear), as I would expect.

hb shows 1 mW tone power at the output port, as I'd expect. This shows up in both the spectrum and time views. (spectrum shown below)

Unfortunately the forum isn't letting me upload more images for some reason, ("an error occurred. Please try again or contact your administrator") but the time sweep view of the hb results shows a 0.63 Vpp waveform at both ports, which matches 0 dBm.

However, the hb tstab waveforms show something else. These show a 240 mVpp waveform at the output port and 390 mVpp waveform at the input port. Neither of these match the harmonic balance result! The same is observed for a transient simulation. I wish I could upload more images to illustrate this, but the waveforms seem to be settled.

So, am I missing something here? Does harm_tuner not work for transient, but somehow does work for harmonic balance, or is something else going on? I understand the nature of harm_tuner will give some weird transients, but the apparently settled behavior for a single tone in transient sim does not seem correct, but then harmonic balance does seem right. I am hoping I can trust the hb results..

I am using IC25.1-64b.38 and Spectre 25.1.0.274.isr6