copyartifact 1.21 fails in at least certain cross-platform copy scenarios

Moved from Copy Artifact 1.20 to 1.21 today, and was greeted with a build-breaking bug. Basic scenario: Windows master, two linux slaves. Build A runs on slave and generates artifact foo/bar.txt . Build B runs and copies the artifacts from build A into directory A-artifacts. A-artifacts directory ends up with a file "foo\bar.txt" (with a literal backslash in the file name), instead of directory "foo" containing file "bar.txt".