Open Ground when on PSW Inverter -- Experts please advise

One of my junk inverters collecting dust in basement actually has voltage at the ground prong at the output. This voltage is about half of the voltage between the two power prongs. So if you are connected to shore power and you plug any three wire appliance into the inverter, you could get shock by touching the appliance with one hand and touching any other appliance like fridge for example that is grounded thru shore power cord. This clearly is a safety issue and I don't want inverter like that in my RV.