[pygtk] glitch in Dialog constructor?

[Alfonso Tarantini]

Greetings everybody.
After deployment of gettext in my application, I encountered this runtime 
error while creating a gtk.FileChooserDialog:

Traceback (most recent call last):
(...)
chooser = gtk.FileChooserDialog(_('Export to PNG...'), self, 
gtk.FILE_CHOOSER_ACTION_SAVE, (_('_Select'), gtk.RESPONSE_OK, 
gtk.STOCK_CANCEL, gtk.RESPONSE_CANCEL))
RuntimeError: first member of each text/response id pair must be a string

It turned out that the object returned by the installed gettext function _() 
called like this:
 _('_Select')
is actually an object of <type 'unicode'> and not of <type 'str'>.
The strange fact is that I can construct a gtk.Button with the 'unicode' 
object as a label and the add_button(...) method in class gtk.Dialog works as 
well:

chooser = gtk.FileChooserDialog(_('Export to PNG...'), self, 
gtk.FILE_CHOOSER_ACTION_SAVE, (gtk.STOCK_CANCEL, gtk.RESPONSE_CANCEL))
select_label = _('_Select')
chooser.add_button(select_label, gtk.RESPONSE_OK)
(this works).

Is this a bug in PyGTK, GTK+, or not a bug at all?
Thank you,
Alfonso Tarantini