When route is changing....?

[K Sun <ksun@essex.ac.uk>]

Hello,
    on page 147 in ns Notes and Documentation (July 1, 1999), there are 
some words about "Session Routing" (the last two lines of 'sesssion 
rouing'), 
"
....
However, the user should note that the instantaneous recompute of the 
routes in the topology can lead to temporary violations of causality 
around the instant that the topology changes.
..
"
   I wonder what "temporary violations of causality" means during "the 
instant that the topology changes"? Under my understanding, it should 
mean:
Because some packets has been delivered in the middle way according to 
the previous route, they might be lost (or ..) after route change has 
been completed. Anyway, in programs, if we realise some codes to 
process such a situation, those packets are still under control.

   I am not sure whether my understanding is right or not. Hope further 
explanation for it.

    Regards,
       Sun Kai