User-Agent:       Opera/9.26 (Macintosh; PPC Mac OS X; U; en)
Build Identifier: 

gdk-property-change() expects a long *parameter when size==32, when running LP64 that means 64bit. Counter-intuitive but that's what X wants. This needs to be changed:
/* transparency and autohide */
static void
_set_transparent (Panel    *panel,
                  gboolean  transparent)
{
    PanelPrivate *priv;
-   guint         opacity;
+   gulong        opacity;

    if (!GTK_WIDGET (panel)->window)

otherwise libX11 will run into a SIGBUS sooner or later, at least on platforms that enforce natural alignment in memory accesses ( as in pretty much anything except amd64 ) 

Reproducible: Always

Steps to Reproduce:
1.build xfce on any 64bit RISC as LP64 binaries
2.watch xfce4-panel crash with SIGBUS
3.



Expected Results:  
SIGBUS

not crash