XEventClass is typedef'd as an "unsigned long", therefore, on an
Alpha, this is a 64-bit long cardinal, i.e. 8 bytes long.
Unfortunately, in the XGetDeviceDontPropagateList function, when the
list of XEventClass entries is allocated, the number of bytes is only
(rep.length << 2), i.e. rep.length*4.  Instead, the proper number of
bytes to allocate for the list would be "rep.length * sizeof(XEventClass).

With the current code, the memory allocated for the list will be
overwritten on a 64-bit machine like the Compaq Alpha.

The function XGetSelectedExtensionEvents (in lib/Xi/XGtSelect.c) uses
the correct computation as suggested above.