Uve, if everyone responds to every item, then the different curvatures of the PCM ICCs will have a slight caterpillar effect on the person measures on the latent variable, but will not alter the rank order of the persons.
In general, we would be concerned if the differences in the curvature of the ICCs caused a change in the rank-order of the item difficulties that impacted construct validity. We would need to ask ourselves, "Which do we trust more: the current data or the construct theory?" Physical scientists would reply "The construct theory, unless the data clearly and convincingly contradict it. In which case, the construct theory needs to be revised."
Suggestion: analyze the items using group-level rating scales as far as possible. Then simulate a dataset of the same size as the current dataset. Analyze the simulated dataset with PCM. How does the variation in ICCs compare with a PCM analysis of the original data?