explicitly defaulted copy constructor is implicitly deleted

[ghost]

/usr/local/mailio/include/mailio/dialog.hpp:213:5: warning: explicitly defaulted copy constructor is implicitly deleted [-Wdefaulted-function-deleted]
dialog_ssl(const dialog_ssl&) = default;
^
/usr/local/mailio/include/mailio/dialog.hpp:196:20: note: copy constructor of 'dialog_ssl' is implicitly deleted because base class 'mailio::dialog' has a deleted copy constructor
class dialog_ssl : public dialog
^
/usr/local/mailio/include/mailio/dialog.hpp:61:5: note: 'dialog' has been explicitly marked deleted here
dialog(const dialog& other) = delete;
^
1 warning generated.

I'm getting this warning which might cause memory leak. Could you please take a look at it? Thank you.