Delivery precondition - no unused imports firing against new work and not checked in files (changeset)

 As Ralph indicates, the client-side preconditions that refer to an Eclipse semantic status (such as no errors or no unused imports) are about the Eclipse status, and not the status of just the change-sets being delivered.   If you want to ignore some your pending changes, you could check those changes into a change set (if they aren't already checked-in), then suspend those change sets, execute your deliver, and then resume those suspended change sets.

This is the intended behavior. The operation is a client side behavior and unused imports only makes sense in the context of a local project that is local on disk. The unused imports and organize imports is an Eclipse capability and does not know or care about change sets. The operation only prevents you from delivering if there are unused imports. You have to fix it and can potentially only deliver additional changes that fix the unused imports.