Grabbing frame from video

This is in continuation of my earlier post where I wanted to pick a color from an Image. Only this time, I wanted to grab a frame from a mpeg2 video and save it as a file so I could submit it to a photo contest. I got a couple of software none of which worked. I then decided to take matters in my own hand and use the Screenshot program in java that I had to take a snapshot of the video while it was paused. There's usually a slight blurring and I was okay with that.
To my amazement, the results were astounding like straight out of a Stephen King novel. First I played my video using Windows media player. Then I paused it at the frame I wanted. Then I ran my Screenshot program to save the frame to a PNG file. So far so good. Now that I had saved the frame I wanted, I let the video play till the end. Then when I checked the saved image guess what I found. The image stored was the last frame from the video and not the frame I wanted to save. It was as if the image got updated by itself after the java program had saved it and exited. How could this possibly be.
I wasn't ready to give up just yet. The last frame got saved to the file since the video kept running till the end. What if I didn't run the video after the file was saved and left it in pause mode. So I tried this out and I got my frame in a image. The picture was still inside of the WMP in the image which I planned to correct using the 'crop' tool of my image editing tool. Again, when I loaded the image into the ImageEditor, the results were frustrating to say the least. The 'crop' function wouldn't work. It was as if the image had a mind of its own and wouldn't respond to my effort to scroll the image. The picture inside the WMP itself would remain stationary while the rest of the picture scrolled. In the end, I decided to make the best use of what I had and just cropped the portion of the image I wanted AND was visible, and saved as a new image. So I had the picture I wanted or so I thought. I closed my ImageEditor and also WMP which was still paused. I was ready to upload the image I had saved to my website. I wanted to check the image before I uploaded it and when I opened it, I was amazed at what I found.

"The image was pitch dark and there was nothing but a black rectangle where earlier there was the picture of a marble structure."

Is there a scientific explanation that has to do with codecs and proprietary video formats or should I treat this as something out of a Stephen King novel.