The annotations were intended for the return
value, not the instance argument.
https://bugzilla.gnome.org/show_bug.cgi?id=731299
/**
* gtk_selection_data_get_data: (skip)
- * @selection_data: (array) (element-type guint8): a pointer to a
+ * @selection_data: a pointer to a
* #GtkSelectionData-struct.
*
* Retrieves the raw data of the selection.
*
- * Returns: the raw data of the selection.
+ * Returns: (array) (element-type guint8): the raw data of the selection.
*
* Since: 2.14
**/