Try moving the mic over to the side of your mouth and about 1" away from it.
my old voice recognition software had a section on best mic placement.

some mic positioning pics - these were the best I could find.
http://www.everythingusb.com/images/...et-compare.jpg
http://www.learnspanishliveonline.com/headset5.jpg


I don't know why it would stop at a certain time...