I think it's more of a measuring and pinning issue. To me it looks like the grey is stretched a bit where the blue is attached, and then the blue was smoothed and stretched a bit when the dark was added,
I use cross grain most of the time and lengthwise grain when I have a fabric pattern that requires it - and do not end up with problems like this. I will measure the border and mark it every 10-15" and also measure the quilt in the same increments and then line up the marks as I sew.