Cloning an issue give only a chance to rename the subject, but keeps all other information.

Used by mantis a clone process means that you get the editor filled with the same text and settings as you had before but with the chance to change the subject and description and other settings. All that is kept is the context (e.g. QtCreator, bug)

In your system a clone just gives a chance to change the subject .....

I think this leads to a very restricted usage.