Hypervigilance (an arousal and reactivity symptom of PTSD) mixed with the negative and distorted thoughts of the cognition and mood symptoms, can lead to being overly critical - of yourself or others. Being overly critical, while in a PTSD rage meltdown, dissociative and/or flashback state, can lead to the put-downs, name calling, and other viciousness that most would call mental abuse. While in that state that is leading to the behavior? There is really not much that the sufferer can do to stop it, and I wouldn't consider it abuse.
It's what comes after, when they are no longer in a symptomatic state - my sufferer would normally apologize and try to figure it out, once he realized, or was told (if he didn't remember because he was dissociating as well), what he did - that makes the episode into either abuse or just that, an episode.
Once the knowledge for the reason behind the behavior is found, I do think that refusing to own your behavior, and your illness, moves on to using the illness as an excuse. Constantly striving to do better, to have a better handle on the symptoms of the illness, and actively working on it, keeps the occasional outburst understandable and forgivable.
