I have several pairs of 7 jeans, and I have the same issue with all of them . . . . the waist stretches after one day of wear.
I don't typically wash my jeans after each use (unless they get dirty).  sometimes I lie to wear jeans without a belt.  This is not possible after one day of wearing them (until I wash/dry them).  Otherwise, they are well made, great color and fit in the legs well.  I prefer my diesel jeans, as they are a little thicker, just as soft and hold the waist size better.