As part of a fix to 1.4.2, the jar command will generate a warning for manifest file sections that are not separated by a newline in the spec. This is different from the 1.4.1 and 1.4.0 behavior which didn't report the warning even though the manifest file was not formatted correctly

eg WARNING: Duplicate name in Manifest: Name

if lines are
Name: class.a
Name: class.b
Name: class.c