OK, you know it is on "the straight of the grain" when they rip it, but that "straight" is really wonky because of the pulling they did to rip it! I always check my fabrics for even-ness by shifting the selvages until the fabric hangs absolutely straight w/o any diagonal gullies showing.
I don't have trouble with ANY of my fabrics unraveling when I pre-wash (which I always do). I'm wondering, do other quilters put their fabrics into the washer on the "regular" dial? I soak my new fabric in hotest water to check for color fastness as well as take care of any shrinking that might want to occur later. I leave it for awhile, rinse if it ran, and add salt or vinegar to set the color. Then I put it in the washer on gentle (now I have a front loader so it is always basically gentle, but I use the "handwash" (most gentle setting) for this step as well as the final washing before gifting), then into the dryer on regular, but put the dial a little low (shorter time) so there is no chance of over drying (which will make a lot of wrinkles). Then I put any fabric that feels damp at all over my wonderful, huge (grandmother's) drying rack and let it dry that way. I don't have to iron it, or cut the non-existent raveled thread off.
I'm saying all this because it seems a lot of people have trouble with pre-washing and unraveling and it simply is not necessary with the cottons we have today. I didn't even have trouble with Walmart's cottons which I bought when I first started quilting, and they were NOT top quality!