I use 505 and it washes out completely, so no stiffness left in the quilt. I have used several basting sprays, including Dritz, and much prefer either 505 or Therm-o-Web. I have seen a few negative posts about Sullivan's, Dritz, and off-brands but do not remember specifics. In one case, it was clear the spray was very old.
Aside from the fact that you may have applied the basting spray too heavily, it may be that there was not enough agitation in your washing machine to get all of the basting spray out. What kind of machine did you use, and what water temp? I know some people have found that they need to use warm water (not cold) and extend agitation time (depending on type of washing machine) in order to get all of the Elmer's glue out of their quilts (Elmer's white washable glue is an alternative basting media to basting sprays). Although Elmer's is water soluble, it doesn't instantaneously dissolve in the presence of water; it still requires some agitation and soap to get it all out. The same may be true of Dritz basting spray.