It very well could have something to do with Active Directory support.  Here's a little getgroups test I used a while back for a previous getgroups issue.  You should see something similar in the output depending on the number of groups in your id.  If it fails, we can eliminate Python from the equation.


#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>

int main(){
    gid_t grouplist[32];
    int n;
    int gidsetsize;

    for(gidsetsize = 0; gidsetsize < 22; ++gidsetsize)
    {
        n = getgroups(gidsetsize, grouplist);
        printf("calling grouplist with gidsetsize = %i, returns %i\n", gidsetsize, n);
    }
    exit(0);
}


calling grouplist with gidsetsize = 0, returns 14
calling grouplist with gidsetsize = 1, returns -1
calling grouplist with gidsetsize = 2, returns -1
calling grouplist with gidsetsize = 3, returns -1
calling grouplist with gidsetsize = 4, returns -1
calling grouplist with gidsetsize = 5, returns -1
calling grouplist with gidsetsize = 6, returns -1
calling grouplist with gidsetsize = 7, returns -1
calling grouplist with gidsetsize = 8, returns -1
calling grouplist with gidsetsize = 9, returns -1
calling grouplist with gidsetsize = 10, returns -1
calling grouplist with gidsetsize = 11, returns -1
calling grouplist with gidsetsize = 12, returns -1
calling grouplist with gidsetsize = 13, returns -1
calling grouplist with gidsetsize = 14, returns 14
calling grouplist with gidsetsize = 15, returns 14
calling grouplist with gidsetsize = 16, returns 14
calling grouplist with gidsetsize = 17, returns 14
calling grouplist with gidsetsize = 18, returns 14
calling grouplist with gidsetsize = 19, returns 14
calling grouplist with gidsetsize = 20, returns 14
calling grouplist with gidsetsize = 21, returns 14