enterprise value question

Thanks for your time!

So I was reading an article where enterprise value was defined as market value of operating assets- market value of operating liabilities. This was broken up into (market value of assets - non operating assets) -(market value of liabilities - liabilities and equity items that represent other investors groups)

Now all this makes sense except for one part to me. the  liabilities and equity items that represent other investors groups part should represent non operating liabilities since liabilities - non operating liabilities should get you to operating liabilities. And it makes sense because debt is included in these items and debt is a non operating liability. However, preferred stock is also include but it is not a non operating liability so how does this make sense? Thanks for any help!