changevar

Hi,
Here is some problem I've found while using the changevar function in the GP calculator. I submit a transcript of the GP/Pari session.Thank you,

GP/PARI CALCULATOR Version 2.0.15 (beta)
                i686 running linux (ix86 kernel) 32-bit version
                (readline v2.2 enabled, extended help available)
                           Copyright (C) 1989-1999 by
          C. Batut, K. Belabas, D. Bernardi, H. Cohen and M. Olivier.
Type ? for help, \q to quit.
Type ?12 for how to get moral (and possibly technical) support.
   realprecision = 28 significant digits
   seriesprecision = 16 significant terms
   format = g0.28
parisize = 4000000, primelimit = 500000
? p=x^5+5*x*y^3+z
%1 = x^5 + 5*y^3*x + z
? poldegree(p)
%2 = 5
? q=changevar(p,[z,x,y])
%3 = 5*z*y^3 + (z^5 + z)
? poldegree(q)
%4 = 3