IMB has completed its second share buyback since it accepted a consultant's report last year that it cancel its ordinary shares through a series of buybacks. The building society announced last week that it had agreed to buy 2.14 million shares at A$4.07 cents a share.The buyback price represents a 10 per cent discount to the deemed market value of the shares (the volume-weighted average price of shares traded over the 10 days prior to the announcement of the buyback).The result was well short of IMB's target, which was a maximum of 14 million shares.The shares purchased represent 5.8 per cent of IMB's shares on issue.In its first buyback, last September, IMB bought 2.9 million shares (7.3 per cent of the shares on issue) at a discount of five per cent.The purpose of the buybacks is to overcome the shortcomings of IMB's hybrid structure; it is a mutual approved deposit-taking institution and also a public company limited by guarantee and shares. The shares are traded on an exempt market operated by IMB.It has around 4000 shareholder members among its 180,000 members.According to last year's consultant's report: "The ordinary shares do not sit comfortably with the mutual structure and present challenges for IMB's board in balancing the expectations of guarantee members and shareholder members."IMB was not in a position to buy back all of its shares at once, because of capital constraints, so the consultants recommended a series of buybacks.