Do you have the remote panel for it? If so, perhaps disconnect it (I think there is a jumper one must install on the 458 if there is no remote panel) and see if it does the same thing... perhaps the panel is going full moron and intermittently turning the inverter on.
1978 Itasca 25RV (sold long ago)
1999 Newmar Dutch Star DSCA36, Diesel Puller, "Dutchess" (for sale)
2001 National RV Marlin 390, Diesel Pusher, "Marlo"