Huneke–Wiegand conjecture and change of rings

Let R   be a Cohen–Macaulay local ring of dimension one with a canonical module KRKR. Let I be a faithful ideal of R  . We explore the problem of when I⊗RI∨I⊗RI∨ is torsionfree, where I∨=HomR(I,KR)I∨=HomR(I,KR). We prove that if R has multiplicity at most 6, then I is isomorphic to R   or KRKR as an R  -module, once I⊗RI∨I⊗RI∨ is torsionfree. This result is applied to monomial ideals of numerical semigroup rings. A higher dimensional assertion is also discussed.