Even in the US, are there any non-DRM examples where reverse engineering for the purpose of interoperability in violation of a license agreement have been used as the basis for copyright claims, even when the results are incorporated into a competing product?

For example, I don't recall Microsoft ever being sued by WordPerfect or Lotus for reading and writing their applications' unpublished file formats, which wouldn't have necessarily involved disassembly or decompilation, but was still the result of reverse engineering that almost certainly involved using a licensed or unlicensed copy of the competitor's product.