Buried in last night's budget paper was a reminder that while the government's backing of the residential mortgage backed securities sector came to an end four years ago, it's likely that the almost A$3 billion worth of top-rated RMBS it still holds will be kept on its books until their issuers redeem them.During the global financial crisis, then Federal Treasurer Wayne Swan directed the Australian Office of Financial Management to invest in AAA-rated RMBS "to support competition from smaller lenders in residential mortgage and small business lending markets," the paper explained.Between 2008 and 2012 the AOFM purchased around A$15.5 billion in high-quality RMBS, which it held until May 2015, at which point the Government announced there would be a progressive sell down of these securities through "a regular competitive auction process, subject to market conditions." Monthly auctions were conducted from June 2015 to October 2015, resulting in total sales of $458 million, in amortised face value terms, according to the budget papers. And then, "heightened global volatility" saw these auctions stall, while the AOFM exercised its discretion "to not proceed with a sale where an acceptable price could not be achieved."As at the end of April 2016, the Government's RMBS portfolio was valued at $2.9 billion, in amortised face value terms. And there it might remain: "In the absence of any further sales, the amortised face value outstanding … is expected to be less than $100 million by around the end of 2020," the budget paper explained.