I2C freeze on Mega 1280

I have a problem with a system of arduinos (master+3 slave), one slave have also active all the four serial. The master scan all the slave with a wire.write to send command than acquire the data with the request. All work correctly for 3 slave but with to one with the 4 serial active (and only if is using it) the i2c freeze the arduino slave and the serial print of the data on the arduino master. Why??

Is possible to block the i2c request on this specific slave when it use the serial?