Strong growth in home loan approvals during the December half-year has been negated, to varying degrees, by borrowers taking advantage of low interest rates to accelerate repayment of their loans. Lenders have reported double-digit growth in approvals but some have struggled to achieve any growth in their mortgage portfolios, as a result of higher prepayment levels.Bendigo and Adelaide Bank reported that its home loan book grew by 2.5 per cent in the six months to December (about half system growth), which led some commentators to assume that the bank was choosing not to compete with the heavily discounted standard variable rates that have been on offer for some months.However, Bendigo and Adelaide Bank chief executive Mike Hirst said the bank was writing a lot of new business - home loan approvals were up 13.5 per cent on the previous corresponding period.Hirst said: "Prepayment on loans is very strong."Wide Bay Australia reported that its home loan approvals increased by 10 per cent in the six months to December, compared with the previous corresponding period. However, the size of its residential lending book increased by just 1.7 per cent.Mortgage lender Homeloans Ltd reported that for the six months to December loan approvals were up 12.4 per cent, compared with the previous corresponding period. However, total funds under administration fell 1.3 per cent.Commonwealth Bank reported that 78 per cent of its home loan borrowers were ahead with their repayments. On average, those customers were seven months ahead of their repayment schedule.Suncorp chief executive Patrick Snowball said Suncorp Bank's customers were repaying faster. He said this was a good thing, in the sense that the credit profile of the mortgage book was improving, but it was making growth difficult.With rates potentially staying low for some time, the high prepayment trend may continue. Lenders may have to pay more attention to the management of mortgage run-offs.UBS banking analyst Jonathon Mott said that credit statistics miss the large flows into and out of the banks' mortgage books and this tended to create an assumption that "the bank that writes the most new business delivers the highest credit growth".In a report on the mortgage market issued last September, Mott said: "This is not necessarily the case. New fundings are the biggest moving part but only one factor."Mortgage flows can be broken down into new funding, redraws, interest and fees, prepayments, property sales and external refinancing. The differences in the banks' mortgage flows have implications for their strategies and growth outlook."According to Mott, some types of mortgages, such as investor loans and interest-only loans, tend to stay on lenders' books for longer.