Type and sort conflicts in semantics are usually resolved by a process of reinterpretation, which introduces an operator into the semantic representation. We elaborate on the foundations of a recent approach to reinterpretation within a framework for semantic underspecification. In this approach, relaxed underspecified semantic representations are inferred from the syntactic structure, leaving space for subsequent addition of reinterpretation operators. Unfortunately, a structural danger of overgeneration is inherent to the relaxation of underspecified semantic representations. We identify the problem and distinguish structural properties that avoid it. We furthermore develop techniques for proving these properties and apply them to prove the safety of relaxation in a prototypical syntax/semantics interface. In doing so, we present some novel properties of tree descriptions in the constraint language over lambda structures (CLLS).