when you train hard and then deload/taper down (take a break/reduce volume) you get fiber conversion. In other words your body begins to super-compenstate and then some converted fast twitch fibers reconvert back to faster and stronger higher threshold type fibers.
If you look at athlete peaking training cycles, you will see many of them take a week off before the big day.
The Man: you have the best avatar ever bro. i am working on gettin gmy post number up there to get that but you beat me to it.
To respond to your question: I routinely take off a full week every 6 weeks or so. It works well for me and I come back stronger every time. I gain the fat just as you described as well. My body needs the breaks and responds well too. I hope this helped. Maybe your body is the same.