I think its more along the lines of confusing the utility function in here:

http://en.wikipedia.org/wiki/File:Model_based_utility_based.png

with the 'function' of the AI as in 'what the AI should do' or 'what we built it for'. Or maybe taking too far the economic concept of utility (something real that the agent, modelled from outside, values).

For example, there's the AIXI whose 'utility function' is the reward input, e.g. reward button being pressed. Now, the AI whose function(purpose) is to ensure that button is being pressed, should resist being turned off because if it is turned off it is not ensuring that button is being pressed. Meanwhile, AIXI which treats this input as unknown mathematical function of it's algorithm's output (which is an abstract variable), and seeks output that results in maximum of this input, will not resist being turned off (doesn't have common sense, doesn't properly relate it's variables to it's real world implementation).