Further to LanX's comments, Data::Dumper knows about the data but not the code that generated it, hence the bless calls instead of method calls to new. This is the simplest way of recreating blessed objects after serialisation.

I assume that the reason there is nothing inside the hashes is that the Gtk2 objects are external data that cannot be accessed by Data::Dumper (or the debugger). Such empty hashes are safer for serialisation and later reconstruction. I've hit issues in the distant past with Gtk objects reconstructed from Storable files. These caused segmentation faults when accessed, presumably because the contents no longer exist at the stored address. Needless to say I don't store references to the Gtk objects in the structures that are to be serialised.