sometimes the pattern is off - sometimes the grain is off - sometimes they both are. this is what happens: the fabric goes through a printing machine. it's held in place on both edges (selvedges) by little teeth on a belt. the belt runs the printed fabric along at an even speed. HAH! that's where the problem is. if the belts on each side are going at even slightly different speeds, the grain is off and it pulls the printed pattern with it. the printed fabric is then treated to maintain the stiffness and color. it also maintains the grain, which is now off. so the pattern is locked in at that angle. since the pattern can't be yanked back where it belongs (because the fabric is wonky), they can't cut with it. it'll never work out no matter what you do. if they try to cut with the pattern, the store is the one that loses 3 - 4 inches on every customer. they can't stay in business that way. years ago, when quality meant something and manufacturing was done here, the grain was much truer. now that companies are sending manufacturing jobs out to non-union countries with little or no oversight, the quality has gone to pot.
it's the fault of the manufacturer. they are responsible for the printing of the fabric. write or email a letter of complaint to them and also complain to the fabric store, and be sure to tell them why. your LQS should NOT be doing business with that company. forget joann's. they'll do business with any company for the right price point.
sorry about the rant. i hope i explained the grain thing in a way that's understandable.