XW4024 - problem with parallel work

Hello from Ukraine
Could you please help to solve following issue with Xantrex / Schneider Electric XW 4024 Invertors? In our country people don't have a lot of experience in that equipment.

Our Customer bought invertor Xantrex XW 4024 (230 V, 50 Hz) about year ago. Right now he bought other XW 4024 to make them work in parallel.

When we switch both invertors to the “invertor mode”, even without any load on them, one of them seems to treating other one as a load: it shows 0,6 kWt load, and it seems that this power goes directly to AC Load L point of the other XW4024.
When one of them in off - everything is fine – consumption is about 0,03 kWt.

1. We connected all wires according to instruction – Xanbus cables, AC Sync cables (pages 2-7, 2-33,34 of the “Installation Guide”). Dev numbers of both invertors where changed, one device was set up as “1Ph Master”, other “1Ph Slave”.
Both invertors are holding same loads, so AC Load L of master inverter were connected to AC Load L of slave, similar was made for AC Load N.

2. We rechecked AC Sync and XanBus cables – and changed them several times, so we are sure problem is not in cable.

3. Invertors are quite old one was manufactured 17 OCT 2008, other 17 NOV 2009.

What could be source of the problem? Thank you