never get on the scale the next day

I don't know if anyone else's bodies are as annoying as mine, but I've begun to notice a trend. I'm not sure if it's scientifically proved yet, but this could help towards "proving".  Any time I run more then 8 miles, I gain weight. It's not noticeable weight, and it's usually anywhere between 2-4 pounds. I get SO frustrated. For example, yesterday I ran 16 miles. I burned a ball park of 1347 calories. That's a ton of calories. Today, I know if I get on the scale I will weigh 2 - 4 pounds heavier then I did yesterday. UGH! It is the ultimate in frustration. Then, by Tuesday, it'll be gone. People tell me it's because the muscles tear and swell and it's probably weight from that. But is that proven? Does anyone else have this issue??