If there is some option that restores the old reasonable behavior in new
GTK2 dialogs, Emacs could set such an option by default.
The old one is still present in GTK, you can set x-use-old-gtk-file-dialog
in Emacs to enable it.
Thanks. I tried to set x-use-old-gtk-file-dialog to t, but even though it
looks like the old GTK file selection dialog, it is completely unusable:
its filename entry field is read-only and even C-l is not available to
enter filenames. It seems the old GTK file selection dialog is intentionally
broken to force users to the new GTK2 file chooser.