Lenders' investor mortgage balances continue to fall, despite all the talk of a recovery in the housing market.According to the latest Reserve Bank figures, total investor mortgage balances fell by 0.1 per cent in September, compared with the previous month, and fell by 0.1 per cent over the 12 months to September.Owner-occupier mortgage balances grew by 0.4 per cent in September and by 4.8 per cent over 12 months.Overall lenders' mortgage balances grew by 0.2 per cent in September and by 4.8 per cent over 12 months. The annual rate of growth is unchanged from August.According to the latest APRA mortgage lending data, ANZ, NAB and Westpac all continue to experience reductions in the size of their mortgage books.Commonwealth Bank is the only big bank to have grown its mortgage book in the past month.ANZ's share has dropped from 15.9 per cent to 14.8 per cent over the past year, according to the APRA numbers. CBA's share has remained steady at 26.3 per cent, NAB's has slipped from 15.9 per cent to 15.7 per cent and Westpac's is down from 25.3 per cent to 24.7 per cent.Lenders that have picked up share over the past year include ING, HSBC Bank Australia and Macquarie Bank.