Section 708.01. Effect of mortgage.

  A mortgage on real property creates a lien on the property mortgaged; except for the lien and subject to s. 708.11 , the mortgagor retains the interest that the mortgagor had at the time of mortgage until that interest is divested by some later act.

An acceleration clause providing that a mortgage becomes due and payable, at the option of the mortgagee, if the mortgaged premises are leased or transferred without its written permission, while not contrary to public policy, is enforceable only in accord with equitable principles governing foreclosure actions. Mutual Federal Savings & Loan v. American Medical Services, 66 Wis. 2d 210 , 223 N.W.2d 921 (1974).