Why klee can't stop after max-time?

[xuzizy]

Hello,   I used klee to run a part of  instrumented coreutils 6.11(cp csplit dir du head mv od pwd shred sort tac tail tsort),and set each of program to run 1800 seconds.But after 16 hours,only 8 programs finished running.This is my args of klee:  klee --libc=uclibc --posix-runtime -output-dir=klee_out_${i}_final -max-time=1800 ./${i}_final.bc --sym-args 0 3 2 --sym-files 0 2 10
Does anyone know what's going on? Please tell me. Thank you.ZhouY