No, they should not leak under those conditions, though it perhaps was extreme. With the slide part way out, look at the outer and inner edges and see if you can see/fell where the rubber molding has come loose from the sidewall.
Notify the selling dealer and also the manufacturer. Tell them you are traveling (that's what Rvs are for, right?) and need warranty service where you currently are, not back at the selling dealer. They should locate another Sandpiper dealer for you to take care of the problem under warranty.