Using collect on countables from mapstats gives a funny result

[mettejoe]

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.