IMB Bank has completed its latest off-market share buyback, paying A$16.5 million to buy 3.49 million shares.This is the fourth buyback in a program that the bank started in 2012 as a way of unwinding its hybrid structure. It is a mutual approved deposit-taking institution and also a public company limited by guarantee. Its shares are traded on an exempt market operated by IMB.A consultant's review commissioned by IMB in 2012 said the ordinary shares did not sit comfortably with the mutual structure and were an expensive form of capital.The consultant said the hybrid structure limited IMB ability to participate in the industry consolidation that was going on at the time and continues today.It recommended buying back the shares in a series of steps and the bank has been doing that ever since, with varying degrees of success.In the latest buyback the bank bought 10.9 per cent of its shares on issue. It has bought about 30 per cent of its shares since the program started.The deemed market value of the shares was $5.50 and a buyback discount of 14 per cent was applied, resulting in a buyback price of $4.73 a share.IMB advised that an ATO ruling is expected to confirm that $3.55 of the buyback price will be treated as a fully franked dividend. The sale consideration per share is $1.95, being a capital component of $1.18 and an additional capital component of 77 cents.