@SimaAdrian The problem is that most other switches from other vendors have the speed parameter on STP fiber links locked to AUTO. Very few models allow the SFP port to be set to "FIXED Speed"....

@Andone Same problem here between T1600G-28TS running 3.0.3 firmware and Allied Telesis switches x510, G950 and AT-FS750. The problem seems to be related with speed negociation on the Fiber Link....