I am learning PETSc following the tutorials of the distribution (version 3.4.1). My question is about the KSPView(ksp,PETSC_VIEWER_STDOUT_WORLD); (line 216) of ex7.c (KSP tutorial). It teaches how to use PCBJACOBI, setting different solvers for each PC block. When I use
mpirun -n 4 ./ex7 -m 20 -ksp_type cg
the output is kind of a mess, like if there wasn't order on the output (and difficult to understand). I just figured out this when I did the serial test
mpirun -n 1 ./ex7 -m 20 -ksp_type cg
Someone can tell me what is going on, since when using PETSC_VIEWER_STDOUT_WORLD the process  should print the outputs of the others processes in some (random) order, but without mixing the outputs?