Just read JP Fokkelman's _Major Poems of the Hebrew Bible_ Vol 1 which
included an analysis of Deut 32. He says on 32:5:
"Although the first sentence of v.5 has probably been subject to some
corruption, the separate elements can be placed easily enough, so that I
will not change the words and translate them as: 'They have spoilt
everything for him, his non-children, because of their blemish.' In case
*lo* indicates the indirect object, the first words mean 'they have treated
him corruptly'. (22)"
footnote (22) to this reads: "The combination 'not-his-sons [-anymore]'
becomes acceptable when we come across this special use of the negation in
v.17a, v.21a and v.21c. The word *muman* I interpret as a causal or modal
adjunct; such an adjunct can be used in poetry without preposition. The verb
in front position does not have to agree with the subject in number."