Whenever a person's special assessment or real property tax obligation, or both, is deferred under this chapter, the amount deferred and required to be paid pursuant to RCW
84.38.120 becomes a lien in favor of the state upon his or her property and has priority as provided in chapters
35.49, 35.50, 36.35, and
84.60 RCW. However, the interest of a mortgage or purchase contract holder who requires an accumulation of reserves out of which real estate taxes are paid has priority to said deferred lien. This lien may accumulate up to forty percent of the amount of the claimant's equity value in the property and the rate of interest must be an average of the federal short-term rate as defined in 26 U.S.C. Sec. 1274(d) plus two percentage points. The rate set for each new year is computed by taking an arithmetical average to the nearest percentage point of the federal short-term rate, compounded annually. That average must be calculated using the rates from four months: January, April, and July of the calendar year immediately preceding the new year, and October of the previous preceding year. The interest is calculated from the time it could have been paid before delinquency until such obligation is paid or the date that the obligation is charged off as finally uncollectible. In the case of a mobile home, the department of licensing must show the state's lien on the certificate of title for the mobile home. In the case of all other property, the department of revenue must file a notice of the deferral with the county recorder or auditor.