Is this a bug of xentrace?

[Hui Kang <hkang@cs.sunysb.edu>]

Hi,
I am using xentrace to trace the events of guest domains on a host 
physical machine.  In the parsed trace file,
if the guest domain is created on the host machine, then the entry is good
switch_infprev    [ old_domid = 0x00000002
// the guest domain has a id of 2.
switch_infnext    [ new_domid = 0x00000000

However, if the guest domain is migrated from another host machine,  the 
parsed trace file shows
switch_infprev    [ old_domid = 0x00007ffff
// the guest domain has a id of 2.
switch_infnext    [ new_domid = 0x00000000
Even the domain Id is 2, it shows 0x00007ffff.
Can anyone explain this? Thanks.