This is the explanation I heard from our Sanskrit teacher in IITK:
The SlOkam was recited a 'paarvatee paramESwarau' for a long time. (I think
this SlOkam figures as an invocation in kaaLidaasu's kumaarasambhavam). The
controversy was this.
jagatat pitarau, vandE paarvatee paramESwarau
The phrase 'pitarau' is in dual number, meaning 'to the two fathers of the
world'. Then the following phrase contradicts this by quoting a woman
(paarvati). How can paaravti be a father of the world? So the common man
consoled himself that the poet meant parents, and not fathers when he said
'pitarau'. Then, some wise guy came to the rescue of kaaLidaasu: he said
kaaLidaasu is not an idiot to write 'pitarau' when he wants to say parents;
he would have said 'maataa pitarau' or some such thing. In this case, he
means exactly what he says: 'to the two fathers of the world, namely
husband of paarvati, and husband of rama' -> hence the split 'paarvateepa
ramESwarau'
Nasy