factor does not work as expected

suppose one has
----factor.max---------------------

display2d : false;

declare(a_1,integer);
declare(a_2,integer);
declare(a_3,integer);

assume(1-xbar_1 > 0);
assume(1-xbar_2 > 0);

assume(a_1 >= 0);
assume(a_2 >= 0);
assume(a_3 >= 0);

h : 
2^(a_2-a_1)*4^(a_3-a_2)*(1-xbar_2)^(a_3+a_2)*(1-xbar_1)^(a_3+a_2+a_1)/8^a_3;

factor(ratsimp(h));
----factor.max---------------------------

maxima -b factor.max

gives
-------output---------------------------
Maxima 5.19.2 http://maxima.sourceforge.net
Using Lisp SBCL 1.0.40-1.fc14
Distributed under the GNU Public License. See the file COPYING.
Dedicated to the memory of William Schelter.
The function bug_report() provides bug reporting information.
(%i1)                          batch(factor.max)

batching /home/user/factor.max
(%i2)                          display2d : false
(%o2) false
(%i3) declare(a_1,integer)
(%o3) done
(%i4) declare(a_2,integer)
(%o4) done
(%i5) declare(a_3,integer)
(%o5) done
(%i6) assume(1-xbar_1 > 0)
(%o6) [xbar_1 < 1]
(%i7) assume(1-xbar_2 > 0)
(%o7) [xbar_2 < 1]
(%i8) assume(a_1 >= 0)
(%o8) [a_1 >= 0]
(%i9) assume(a_2 >= 0)
(%o9) [a_2 >= 0]
(%i10) assume(a_3 >= 0)
(%o10) [a_3 >= 0]
(%i11) 
h:2^(a_2-a_1)*4^(a_3-a_2)*(1-xbar_2)^(a_2+a_3)*(1-xbar_1)^(a_1+a_2+a_3)
          /8^a_3
(%o11) 2^(a_2-a_1)*4^(a_3-a_2)*(1-xbar_1)^(a_3+a_2+a_1)*(1-xbar_2)^(a_3+a_2)
         /8^a_3
(%i12) factor(ratsimp(h))
(%o12) 2^(a_2-a_1)*4^(a_3-a_2)*(1-xbar_1)^(a_3+a_2+a_1)*(1-xbar_2)^(a_3+a_2)
         /8^a_3
(%o12) "/home/puck/factor.max"
-------output---------------------------

1. Question:
Is it possible to force maxima to combine the integer powers?

2. Question:
How can I extract the exponents of (1-xbar_1) respectively (1-xbar_2)?

Thanks
Andre