Using collect on countables from mapstats gives a funny result

I have the following code

human_mapped = map(input, reference='hg19')
mapping_statistics = mapstats(human_mapped)
collect(mapping_statistics,
current=sample,
allneeded=samples,
ofile=QCDIR </> 'mapping_to_human.txt')

In the output file I get the following
sampe_1 sample_2 sample_3 sample_4 sample_5
total 39084 0 0 0 0
aligned 745 0 0 0 0
total 0 37051 0 0 0
aligned 0 4615 0 0 0
total 0 0 35219 0 0
aligned 0 0 13042 0 0
total 0 0 0 39876 0
aligned 0 0 0 805 0
total 0 0 0 0 34963
aligned 0 0 0 0 7
unique 744 4600 12994 805 7

I would have expected 3 rows (total, aligned, unique) instead of 11 rows.

Start by reproducing the mapstats and collect snippet from the issue and inspect the collect handling for countable mapping statistics. Compare the generated table with the expected three rows—total, aligned, and unique—and use that output difference to locate the relevant implementation or tests.