=== modified file 'src/rail_gui.cpp'
--- src/rail_gui.cpp	2008-04-22 18:36:42 +0000
+++ src/rail_gui.cpp	2008-04-30 13:48:31 +0000
@@ -748,7 +748,7 @@
 	if (!ValParamRailtype(railtype)) return;
 
 	// don't recreate the window if we're clicking on a button and the window exists.
-	if (button < 0 || !(w = FindWindowById(WC_BUILD_TOOLBAR, 0)) || w->wndproc != BuildRailToolbWndProc) {
+	if (button < 0 || !(w = FindWindowById(WC_BUILD_TOOLBAR, 0)) || !w->CompareWndprocEqual(BuildRailToolbWndProc)) {
 		DeleteWindowById(WC_BUILD_TOOLBAR, 0);
 		_cur_railtype = railtype;
 		w = AllocateWindowDesc(&_build_rail_desc);
@@ -1598,7 +1598,7 @@
 		Window *w;
 		_last_built_railtype = _cur_railtype = RAILTYPE_RAIL;
 		w = FindWindowById(WC_BUILD_TOOLBAR, 0);
-		if (w != NULL && w->wndproc == BuildRailToolbWndProc) {
+		if (w != NULL && w->CompareWndprocEqual(BuildRailToolbWndProc)) {
 			SetupRailToolbar(_cur_railtype, w);
 			SetWindowDirty(w);
 		}
@@ -1649,7 +1649,7 @@
 
 	_last_built_railtype = _cur_railtype = rt;
 	Window *w = FindWindowById(WC_BUILD_TOOLBAR, 0);
-	if (w != NULL && w->wndproc == BuildRailToolbWndProc) {
+	if (w != NULL && w->CompareWndprocEqual(BuildRailToolbWndProc)) {
 		SetupRailToolbar(_cur_railtype, w);
 		SetWindowDirty(w);
 	}

=== modified file 'src/window.cpp'
--- src/window.cpp	2008-04-19 13:39:00 +0000
+++ src/window.cpp	2008-04-30 14:07:31 +0000
@@ -46,6 +46,19 @@
 
 byte _special_mouse_mode;
 
+/**
+ * Check whether the window uses a particular window event handler function
+ * @param proc Window handler function to compare with
+ * @return \c true if the window uses the provided window handler function,
+ *         \c false if not
+ *
+ * @note The check is used as a way to distinguish between different windows
+ *       in the same WC_BUILD_TOOLBAR window class
+ */
+bool Window::CompareWndprocEqual(WindowProc *proc)
+{
+	return wndproc == proc;
+}
 
 void CDECL Window::SetWidgetsDisabledState(bool disab_stat, int widgets, ...)
 {

=== modified file 'src/window_gui.h'
--- src/window_gui.h	2008-04-19 13:39:00 +0000
+++ src/window_gui.h	2008-04-30 13:46:27 +0000
@@ -339,6 +339,8 @@
 	void CDECL SetWidgetsHiddenState(bool hidden_stat, int widgets, ...);
 	void CDECL SetWidgetsLoweredState(bool lowered_stat, int widgets, ...);
 	void InvalidateWidget(byte widget_index) const;
+
+	bool CompareWndprocEqual(WindowProc *proc);
 };
 
 struct menu_d {