I'm using Revit 2019.

I have piping that I create in Revit, using Fabrication... regardless if I draw Revit Piping, then convert via Piping to Fabrication option, or build it directly using Fabrication, I've tried this both ways, same result...

Anyway, I build this piping, and I select all of it, and I want to set it to be "Existing" by changing the "Phase Created" to Existing.

All is good so far. 

If I grab all that same piping, and set it to be demolished by setting the Phase Demolished to Demo (or any level for that matter) I get this "action necessary" prompt about how things need disconnected. If I "ok" through that, I lose all my flanges, and weld gaps.

I tested with just a weldneck flange, pipe and an elbow and this is what I got.

I exported the error report and I snipped my screen with it.

Is doing Demo phasing not an option with Fabrication parts?