The extension manager uses the service
com.sun.star.registry.ImplementationRegistration to register services.
The revokeImplementation function does not delete all the entries which are
created by registerImplementation. For example registerImplementation created
these entries:

/
 / IMPLEMENTATIONS
   / com.sun.star.comp.extensionoptions.OptionsEventHandler$_OptionsEventHandler

     / UNO
       / ACTIVATOR
         Value: Type = RG_VALUETYPE_STRING
                Size = 26
                Data = "com.sun.star.loader.Java2"

       / SERVICES
         / com.sun.star.comp.extensionoptions.OptionsEventHandler
       / LOCATION
         Value: Type = RG_VALUETYPE_STRING
                Size = 103
                Data = "vnd.sun.star.expand:$UNO_SHARED_PACKAGES_CACHE/uno_packa
ges/4AF3.tmp_/leaves1.oxt/extensionoptions.jar"

 / SERVICES
   / com.sun.star.comp.extensionoptions.OptionsEventHandler
     Value: Type = RG_VALUETYPE_STRINGLIST
            Size = 84
            Len  = 1
            Data = 0 = "com.sun.star.comp.extensionoptions.OptionsEventHandler$_
OptionsEventHandler"

After calling revokeImplementation there is still:

/
 / SERVICES
   / com.sun.star.comp.extensionoptions.OptionsEventHandler
     Value: Type = RG_VALUETYPE_STRINGLIST
            Size = 84
            Len  = 1
            Data = 0 = "com.sun.star.comp.extensionoptions.OptionsEventHandler$_
OptionsEventHandler"