[Discuss] Weird awk processing

[darose at darose.net (David Rosenstrauch)]

Just stumbled upon the most bizarre awk problem.  mawk and gawk are 
showing 2 different results for the same code.  Can anyone shed any light?

TIA!

DR

---

sense at ip-10-98-190-45.job:/sense/work/feature-summary/debugging$ cat 
sample.txt
32e49398e024dcb79a319c62ceb213ae3e824f77        2
32e4cb91fdefe6103d73f1d6e43ecd8430f85334        2
32e4cb91fdefe6103d73f1d6e43ecd8430f85334        132
32e5434c41a8e2f0178fd19bd868758af6eb67c0        2
32e56067        10
32e56067        79
32e56122        59
32e57aacfd27f7fde61184052cb35551213c7cd6        5

sense at ip-10-98-190-45.job:/sense/work/feature-summary/debugging$ cat 
../totals-by-label.awk
#!/usr/bin/awk -f

BEGIN {FS="\t"; prev_label = "";}
{
         curr_label=$1;
         count=$2;
         if (prev_label != "" && curr_label != prev_label) {
                 output();
         }
         prev_label=curr_label;
         tot += count;
}
END { output(); }

function output() {
         print prev_label"\t"tot;
         tot = 0;
}

sense at ip-10-98-190-45.job:/sense/work/feature-summary/debugging$ cat 
sample.txt | mawk -f ../totals-by-label.awk
32e49398e024dcb79a319c62ceb213ae3e824f77        2
32e4cb91fdefe6103d73f1d6e43ecd8430f85334        134
32e5434c41a8e2f0178fd19bd868758af6eb67c0        2
32e56122        148
32e57aacfd27f7fde61184052cb35551213c7cd6        5

sense at ip-10-98-190-45.job:/sense/work/feature-summary/debugging$ cat 
sample.txt | gawk -f ../totals-by-label.awk
32e49398e024dcb79a319c62ceb213ae3e824f77        2
32e4cb91fdefe6103d73f1d6e43ecd8430f85334        134
32e5434c41a8e2f0178fd19bd868758af6eb67c0        2
32e56067        89
32e56122        59
32e57aacfd27f7fde61184052cb35551213c7cd6        5