I think it seems that unhealthy introverted perceivers (i.e. those who fall back on their tertiary function too much) could easily mistype themselves as introverted judgers. Js are described as people who make decisions easily and can be stubborn toward the opinions of others, and an unhealthy P is exactly this; one who falls back on introverted perceiving to convince themselves that they don't have to consider and participate in the outer world.
An unhealthy IP could easily have conditioned themselves to take a cocooned stance with the world if they feel it isn't worth participating in (for whatever reason), which can result in behaviour that can easily lead to this sort of mistyping. I suspect this is the reason that I found it hard to decide my type at first because I have conditioned myself to be very suspect of others and their dealings toward me.
I'm not sure if this happens the other way around, either; an IJ is likely to be very decisive regardless of their outlook, its just a case of what they decide to do with their perceptions. e.g. healthy INTJs tend to preach "taking responsibility and doing you part in the community rationally" (auxillary Te) since they know that funneling Ni into their tertiary function (Fi) can lead to selfish and potentially disastrous results. This sort of lesson is often learnt from first-hand experience.
Has anyone else encountered this? I've often read posts from other members and wondered if this has happened to them without them knowing about it.