banks do this all the time. ANZ tried it on me once on one of my loans and I simply moved to ING.
I got a call from the ANZ retention team asking why i left, and when i said that is because i wanted to go IO on a P%I loan after a 5 year fixed term and the bank refused they wanted me to come back because 'i didnt speak to them 1st': would i like to come back?, umm no.
my loans are with all the big 4 and ING.
if you are paying the loan, and selling would return negative equity... would you force a sale on your customer??