On Windows, when a key-press-event is received after the user presses Shift, Ctrl or Alt, the GdkEventKey.is_modifier flag is 0.  It should be 1.

To see the problem, build the following program and press a key such as Shift.  I'm using GTK 2.18.3 on Windows 7.

== test.c ==

// build with: gcc -Wall test.c `pkg-config --cflags --libs gtk+-2.0` -o test

#include <stdio.h>
#include <gtk/gtk.h>

static gboolean key_press_event(GtkWidget *widget, GdkEventKey *event) {
    printf("is_modifier = %u\n", event->is_modifier);
    return TRUE;
}

int main(int argc, char *argv[]) {
    gtk_init(&argc, &argv);

    GtkWidget *window = gtk_window_new(GTK_WINDOW_TOPLEVEL);
    gtk_widget_show_all(window);

    g_signal_connect(G_OBJECT(window), "key-press-event",
                     G_CALLBACK(key_press_event), NULL);

    gtk_main();
    return 0;
}

== end ==