Collapse tool question

The "collapse" tool is useful for generating static geometry from parametric features.  Often, I copy the surfaces of a sub-component and then collapse the copy feature so that I can be free to move the resulting independent geometry feature "up the model tree" and use it as a visual reference.

(screenshot above is from assembly mode)

Thing is, sometimes this tool is not available (it is grayed out).   I am not sure about what are the conditions for its availability.

I think it depends on whether the model is used in another assembly (that is in session) and also seems affected by presence of family table instances / models made "flexible". 

Does anyone have similar experience?  I'm still on Creo4, BTW.