Working with phases is a great tool that I have been taking advantage of, however I have noticed in MEP 2012 that when an item is demolished, the properties for 'System Classification' and 'System Type' are lost.
Example: I am drawing existing supply air ducting for a renovation project. The phase I am drawing in is the existing phase. I then move to the new construction phase to demolish some old duct from the existing system, and then draw the new supply air duct. When I demolish the existing supply air duct, the the demolished duct's properties of System Classification and System Type go from "Supply Air" to "Undefined". This is a problem for me because it is a loss of information that I wish to keep in the model. If I change the demolished duct property of 'Phase Demolished' from New Construction to None, essentially undemolishing the item, the System Classification and System Type properties are stuck in "Undefined" and never do regain their Supply Air status. This could pose a problem if I accidentally demolished something that I did not mean to. That item demolished by mistake would not be recovered, and would have to be deleted and redrawn.
Also, regarding the phase graphic overrides, would it be possible for a demolished item to be displayed with a phase graphic override of the various dotted lines and colors, for different systems that would be demolished? Would the demolished phase graphic overrides be able to be a part of each system, so that a Supply Air demolished duct would look different than a Return Air demolished duct?
I am having the same problem. Demo'd items changing their 'System Classification' and 'System Type' to undefined creates an issue for me when I have separate domestic water and sanitary plans. My filter originally allowed me to only see systems that I wanted, but once I phase them to be demo'd, they lose their classifications and show back up on ALL of the similiar plans. To get around this (although the preferred method would be to simply regain system classifications), I created worksets that I use as filters. Simply create a workset and apply all similiar items that you want to filter to that workset. Under Visibility Graphics_Worksets, change that workset to hide. You will have to do this on all of the sheets that your undefined elements show up on, but this process to filter them out shouldn't be too painful. Hope this helps...
TO AUTODESK: Is there a way to keep systems classifications on items that are being phased? This has been quite inconvenient!
In MEP 2012 it use to at least keep System Abbreviation but now with MEP 2013 it is gone as well. All demoed systems should keep system information. It would be very nice if the demoed items could remained connected too.