The type of INFJ you are describing is one that has taken on the bad aspects of an ESTP, or an ENFP, depending on what kind of trama they have indured and for how long.
If you have an INFJ who is an an ESTP mode it is likely caused by long term stress from things in their external life. Money issues, relationships, bad luck, ect. If this goes on long enough they enter this mode. It is pretty much a way for the INFJ to get certainty, and instant gratification. As being like a bad ESTP it allows the individual to get satisfaction in the short term to mask out the hurt they are feeling. To the external observer the INFJ would appear very much like an ESTP (depending on the degree of the shadow mode, the true INFJ nature may or may not be visiable). The distinction between an INFJ in shadow and a true ESTP is how the INFJ feels while this is going on, and how they feel after words. An INFJ in shadow ESTP mode will likely feel detatched, almost as if they watching themselves do the things they are doing. They could in essence, rob a store and punch the person they are robbing, then after the ordeal, wonder to themselves "...did I actually just do that? It feels so surreal..." they will have the urge to process it beyond that, but something stops them from being able to do so. An INFJ in shadow mode also isn't there 24/7, when the individual exits the mode for a short time, it is usually a very depressive mode and they ask themselves "why is all of this happening". Full relization does not come about until they have fully exited shadow mode.