what does the contents of that manifest.mf say what version it is? i guess 1.2?
Manifest-Version: 1.0
Application-Name: log4j.jar
Bundle-Description: Apache Log4j 1.2
Bundle-License: http://www.apache.org/licenses/LICENSE-2.0.txt
Bundle-SymbolicName: log4j
Built-By: cy
Bnd-LastModified: 1336302107501
Bundle-ManifestVersion: 2
...