It has to do with how the inverter "decides" what the proper loading on the source is to determine the peak power operating point.

 Since the inverter in question is designed to work with PV the MPPT algorythm is designed around the electrical charactoristics of PV panels. (MPPT stands for maximum power point tracking.)

 The PPV  (peak power voltage) of a pv panel varies mostly with cell temperature, and changes relatively slowly

 To my knowledge the algorythms used (in battery-less grid tie PV inverters) for finding the MPP of a PV array are based on:

 (1) Periodically sweeping the range of operating voltages for the PV array and then returning to the best operating point.

 (2) Dither, i.e.  move the operating point slightly up or down the voltage current curve, if the power increases continue in the same direction, if the power decreases move in the opposite direction.

 (3) Momentarily unload the panel to check the open circut voltage (which varies with temperature also) then back down X % to the approximate PPV.

 The exact algorythm for a given PV inverter my be a combo of these or some other method I am unaware of, and is usually proprietary.

 For MPPT of wind methods 1 and 3 will not work for obvious reasons (at least to me).

 The dither method of  2 would appear to work at first glance. However unless the momentum of the wind turbine is taken into account (different for each wind turbine design) increasing the load will take kinetic energy out of the system and always appear "better" on a momentary basis driving the turbine into stall.

 The obvious question is what if the inverter doesn't  "try " to track MPP.

 This will work fairly well and is what you end up with when using a battery based grid tie inverter. (note the different power curves for the AWP turbine for battery charging and high voltage grid tie, this is due to the better load matching of the grid tie model). To my knowledge there is no way to "trick" the inverter in question into this operating mode.

 Again, the easy way to accomplish wind grid tie will be with either a battery based Grid tie inverter such as Outback (easiest)or the high voltage SMA windy boy route. The windy boy is a sunny boy inverter with a wind turbine loading algorythm, it must be programed for a given turbine by the distributer (you will need to tell them the "slope" of the load line) and protected from over voltage.