Yes, I often have this reaction. It actually helps because by the time I am ready to react to the situation, the event is usually past and I am better able to deal with my emotions if the event is over.
A few years ago, I had just gotten past a really stressed out period where I had to deal with a difficult relative, and with being homeless for several months. Not long after my homeless period was over, and things were looking up, I finally had Medicaid, so I finally had a female bleeding problem taken care of. The doc called me a week later and said I had cancer. He was upset, but I was super calm because I just wasn't able to react at the time, I had used up most of my upset juice while being homeless, so I wasn't able to muster enough to seem upset immediately upon being told of the cancer diagnosis. This weird calmness helped me focus on researching my situation, and helped me through a complete hysterectomy, and radiation treatments. I am now cancer free. The annoying female bleeding problem that led to the discovery of my cancer actually saved my life. This kind of cancer is often not found until it's too late, but the second biopsy, after the hysterectomy, said that it was a very bad form of cancer, but that they had caught very early, before it had a chance to spread.
I think if I had reacted more emotionally at the time, it would have interfered with my getting through this tough time.
There is a down side to appearing to be unemotional at stressful times. People often think you don't care, and it hurts their feelings. The truth is, it takes us on the spectrum longer to process input, and to formulate a proper output. While we are slogging through the process at snail speed, we appear to be unemotional. Also, we are not good at faking emotional responses regarding things and people not very close to us, but NT people still expect those responses.
In spite of the problems it causes, I think I prefer the longer processing time for emotional responses. I am better able to handle problems when the events are already over, or when I have had more time to absorb the situation.