Removing an item of an enumerated array

I want to remove an array item from an enumerated array. The enumeration class 'ValueFlag' is derived from int16.

a = ValueFlag([5;5;9;0])

a(3) = []; % this results in an error a(2:3)=[]; % this of course also...

Is there a way to delete array item out of an array of an self defined enumerated type? Do i have to overload subsasgn() an how can that be done without running into massive problems?