pylint #36652 Arguments incorrectly marked as unused if the "+=" operator is used on them [open]

The following program

def append(listVar):
    listVar += [ 1, 3 ]

l = [ 2 ]
append(l)
print l

produces this on 0.21:
W0613:  2:append: Unused argument 'listVar'
prioritynormal
typebug
done in<not specified>
closed by<not specified>