Hi Alun
You are not alone with this issue. Try setting your shadow warning level to 2, rather than 0, and you should start to get reliable warnings.
That's right, increase the threshold and clipping indication will be able to show lost information.
For some reason, C1 Pro does not indicate shadow clipping when level is set to 0.
Technically that is correct, because R/G/B zero doesn't mean it is clipped, maybe it's just zero. The lowest signal levels will have relatively more noise, to the point that the noise threshold exceeds the detectable signal levels (significant noise level above and below the signal level). So it is hard to say what is clipped signal, and what is noise. So by deliberately stating that the signal threshold should be above zero, we will have some signal (and noise) that is lower than that, and it can then be labeled as 'clipped' if below.
An output clipping indicator is not the same as a threshold indicator. And there is also the issue of Gamma, a linear gamma (Raw) signal of 1 (in 255), may be 20 (in 255) after gamma 2.2 precompensation. So it also depends on what exactly triggers the indicator and at how many bits of precision it is calculated. If 14-bit accuracy were used, due to the 14-bit Raw sensor signal, then 1 would roughly be 3 after gamma precompensation, and at 16-bit precision it would round up to 2.
Cheers,
Bart