BCEL Repository.lookupClass can't find dynamically generated classes

Recently I used Apache BCEL (Bytecode Engineering Library) to modify classes and load the altered versions. That process starts with Repository.lookupClass call to get a BCEL JavaClass instance representing a class. However, when I tried to do that to a dynamically generated class (actually one that had already been through an editing process) rather than one loaded normally by the system classloader, it couldn't find the class. If I understand correctly, lookupClass searches the application classpath and loads a .class file from disk? That will clearly not work for anything dynamically generated, so the alternate route of passing a byte stream to ClassParser is needed. This works if you can keep track of the bytecode of the edited classes you create, but isn't possible for classes created by others.