The managed fund buys and sells shares etc as part of it's operating activities. If the net of all the sales results in a profit then you have a capital gains event which you show in your ITR. If you sell your units in the fund at a profit you then have a capital gain.
I can understand your thoughts of paying capital gains twice but think of it this way:
Fund has income of 100 interest and 100 capital gain ie total income 200
Fund has income of 200 interest only ie total income 200
The net result is the same, you have to declare 200 of income
The benefit of having a capital gains component is that you can offset it against any capital losses you may have
