Timeout STate for Digital Out Modules

Currently I am working with a Digital Output block in UnityPro. When I select the Timeout State as User Defined value my application is defined to use the direct addressing i.e. %Mx for this module. But when the timeout state is Hold Last value the topological address %Q is being defined. Is this correct?

If not then what should be the right way? If yes then what is the real reason behind this feature?