Kohl's cash online AFTER return?

Hello. I purchased some items and received $20 in Kohl's cash. I returned them yesterday (used Kohl's card) and received an email saying I had Kohl's cash to use. I went to "use" it as a test and it appears that it will actually work (without checking out). Does anyone know the policy on this? I've never used Kohl's cash before and have no idea why it wouldn't be invalidated? Thanks.