In a case that has echoes of the court action started by Pioneer Mortgage Services earlier this year, Queensland State Home Loans (QSHL), is preparing to sue Columbus Capital in a dispute over the terms of agreement covering a portfolio of mortgages.In a statement of claim lodged last month by QSHL, at the Federal Court in Sydney, and sighted by Banking Day, it is alleged that Columbus Capital "unilaterally" moved to change a crucial reference rate. On QSHL's numbers, this action is costing it around $50,000 per month in lost management fees.The claim document, which seeks damages, interest costs and "such other orders or relief as the Court thinks fit", sets out a complex history, tracking through several versions of a mortgage origination and management deed (MOMD). The MOMD in question was first set up in 1992, and was varied several times up to 2008 by negotiation between several parties, including Firstmac founder Kim Cannon, who has a controlling interest in QSHL.The QSHL document outlines how, in 2001, the company started providing mortgage origination services to an ANZ distribution business, Origin Mortgage Management Services. Under the terms of the MOMD, ANZ paid fees to QSHL based on the difference between what the borrower paid and what the parties called the "mortgage manager delivery rate". This latter rate was calculated by adding a "base margin" of 75 basis points to ANZ's "funds transfer pricing rate", or FTPR. This was the monthly average of the 30-day swap rate plus a "liquidity margin" of 11 bps, and was "notified by ANZ to QSHL from time to time". In 2008, ANZ and QSHL entered into a new MOMD, which varied some clauses.In September 2012, ANZ transferred its rights and obligations, along with the portfolio of loans originated by QSHL, to Columbus Capital. Two months later, Columbus wrote to QSHL, the company alleges, advising that the mortgage manager delivery rate was to be increased by 160 bps, effective from December 1, 2012, but the cost would not be passed on to borrowers. As the management fees payable to QSHL were based on the difference between the rate paid by the borrower and the mortgage manager delivery rate, this would have the effect of severely reducing QSHL's fees.The crux of the legal action, as outlined by the QSHL statement of claim, is to determine which of the clauses in which of the MOMDs should apply. QSHL, not surprisingly, is pushing for the clauses that were in place in 1998, while arguing that Columbus has no right to apply what it calls a "revised FTPR delivery rate". (Incidentally, according to presentation quoted by QSHL in its claim, this formula will favour a mortgage portfolio manager in a time of falling interest rates.)A schedule provided by QSHL claims it missed out on $343,595 in fees between December 1, 2012 and June 30, 2013.Columbus Capital, a mortgage provider and funds manager, is not expected to file its response until mid-October, ahead of the parties' first day in court, which