I've found too that normally I can detach, but some things create a visceral response to me. When I was working my first job twenty years ago, a guy was friends with someone on the EMT squad in our local rural area, and he came into work with Polaroids of an incident where a small plane had crashed on a house in town (right during rush hour -- the pilot had a heart attack, and the plane went down and totaled the house, killing the passengers and the old couple living there). I ended up looking at them, mostly out of morbid curiosity, and while my brain seemed to "parse" everything in a detached way, recognizing what it was, etc., I found my body actually responding to the pictures negatively, without any conscious understand of why -- kind of like if you get hurt, you yell/lash out. it was purely automatic. I found myself getting dizzy and nauseated, and I could't get the images out of my mind.
So even if you understand what has happened, it's still likely that you are responding to the incident on a more basic level. it's not weird to have a lingering reaction where something really bothers you.