Got into an interesting issue with M4 ethernet backhaul with the following simple setup:

ISP -> M4 router mode -> L2 dlink dgs-1100-08 switch (zero configuration, no other devices connected) -> M4 AP's

In this case main M4 doesn't provide internet to WiFi clients after the roaming (connected without internet). Rest AP works as expected. 

As soon as M4 AP's are disconnected from the switch (e.g. no ethernet backhaul), main M4 starts operating normally. 

Without the switch, if I connect one M4 AP directly to the main M4 (second ethernet port) then everything working fine as well. 

So it is clearly a switch issue. Only God knows why but I've tried to experiment with trunking, vlans, etc. and it doesn't do anything. 

Do I miss something? Some switches doesn't support roaming? What switches you guys using? 

Thanks.