OK, the way I understand it, virtual parts are saved in the Windows "Temp" folder until the assembly is saved and then the virtual parts are saved in the assembly file. I am having problems with virtual parts disappearing so I did some investigating.
I created a virtual part in an assembly while monitoring the Windows "Temp" folder. In the image below you can see the virtual in the SW assembly and in the Windows "Temp" folder.
I saved the assembly and refreshed the Windows Explorer window... The virtual part is still in the "Temp" folder?
I closed the assembly and the virtual part disapears from the Windows "Temp" folder.
I reopen the assembly and I get the following
My Windows "Temp" folder is located on a RAM drive but I don't think this matters unless I turn off my system.
So what am I missing here?