When you move the beginning of a caption ahead of it's end, by typing the time stamp, it closes the program.
We have completely redesigned the captioning workflow in Premiere Pro version 15.0. You will see this feature as well as many other dramatic workflow improvements. Please update to the latest version.
Learn all about the new captions workflow here: https://helpx.adobe.com/premiere-pro/user-guide.html/premiere-pro/using/working-with-captions.ug.html