Just to make sure I didn't ommit some strange XisbNew caller I annoted
every piece of code that id-utils found like this:

...
programs/Xserver/hw/xfree86/input/spaceorb/spaceorb.c:97:        "XisbNew",
programs/Xserver/hw/xfree86/input/spaceorb/spaceorb.c:226:	priv->buffer = XisbNew (pInfo->fd, 200);
programs/Xserver/hw/xfree86/input/spaceorb/spaceorb.c:227:	xf86Msg(X_ERROR,"%s:%d: XisbNew() -> %p\n", __FILE__, __LINE__, priv->buffer);
programs/Xserver/hw/xfree86/input/ur98/xf86Ur-98.c:38:	"XisbNew",
programs/Xserver/hw/xfree86/os-support/bsd/bsd_mouse.c:574:	    pMse->buffer = XisbNew(pInfo->fd, pUsbMse->packetSize);
programs/Xserver/hw/xfree86/os-support/bsd/bsd_mouse.c:575:	    xf86Msg(X_ERROR, "%s:%d: XisbNew() -> %p\n", __FILE__, __LINE__, pMse->buffer);
programs/Xserver/hw/xfree86/os-support/hurd/hurd_mouse.c:118:	    pMse->buffer = XisbNew(pInfo->fd,
programs/Xserver/hw/xfree86/os-support/hurd/hurd_mouse.c:120:	    xf86Msg(X_ERROR,"%s:%d: XisbNew() -> %p\n", __FILE__, __LINE__, priv->buffer);
programs/Xserver/hw/xfree86/os-support/sunos/sun_mouse.c:235:	    pMse->buffer = XisbNew(pInfo->fd,
programs/Xserver/hw/xfree86/os-support/sunos/sun_mouse.c:237:	    xf86Msg(X_ERROR,"%s:%d: XisbNew() -> %p\n", __FILE__, __LINE__, priv->buffer);

but none of this logs is executed. The only log I see is:

...
(II) XINPUT: Adding extended input device "Mouse0" (type: MOUSE)
(EE) XisbNew called
(EE) XisbNew() returning 0x899b860
Could not init font path element /usr/X11R6/lib/X11/fonts/Speedo/, removing from list!
Could not init font path element /usr/X11R6/lib/X11/fonts/CID/, removing from list!
(EE) XisbBlockDuration(0x10)

 -> and *boom* it dies.

So - where is XisbNew called? Am I missing some loader magic? A function
pointer?

Martin