I used Elmer's to baste two quilts recently - diluted - so that may be the problem. On one, you can't tell. On the other - I can see markings from the glue on the backing. As both are quilts, not wall hangings, they will be washed - but you may want to take a look and see if you can see the glue. On the one, I may have over-diluted. Or it could be the backing - which was an old bed spread - so I'm not sure of the fabric content - just that it is sturdy and will work well for a picnic quilt.
Cheers, K