HI....It isn't unexpected to interface the Neutral to earth at any force source and no what other place. As it is preposterous without extremely unique gear fit for framing two separate supplies, to have more than one AC source at any one time, at that point the nonpartisan ought to be grounded at the inverter, This may be a current inward association, and is easy to check with an ohmmeter - 0 ohms earth to ground at the inverter outlet with nothing else associated.
Assuming you don't ground the unbiased, the nonpartisan can buoy to any voltage, and this could mean a danger if the impartial line got shorted to a non-earthed piece of metalwork some place.