This happens when the default is a raw IPP queue which points to an IP address which does not exist in the network, as the dialog asks CUPS for the properties of the selected printer (which is the default printer in the beginning) and the appropriate CUPS library function sees a raw IPP queue and for this it assumes that it is a printer on a remote CUPS server and tries to get the PPD from there. Then it tries to access the remote CUPS server without forking a sub-process and without setting a very low timeout (if this is possible).
This is a bug of the CUPS library, as it happens also with non-GNOME/GTK clients.
This happens when the default is a raw IPP queue which points to an IP address which does not exist in the network, as the dialog asks CUPS for the properties of the selected printer (which is the default printer in the beginning) and the appropriate CUPS library function sees a raw IPP queue and for this it assumes that it is a printer on a remote CUPS server and tries to get the PPD from there. Then it tries to access the remote CUPS server without forking a sub-process and without setting a very low timeout (if this is possible).
This is a bug of the CUPS library, as it happens also with non-GNOME/GTK clients.