Strange behavior of DIGI ME on uart out, if no real driver active

May be anyone can give a hint.
We use the Digi ME in a multi interface application. (LAN, USB-serial, RS232, TTL-UART e.t.c)
The embedded processor from our application sends serial data (standard baudrates) to all attached serial interfaces at the same time.
Incoming serial data from all serial interfaces are ANDed - so the embedded processor can interpret the data from any serial port.
This works well…
But, if the embedded processor sends data and the DigiME is not serviced
by RealPort or so after sending 64kByte the DigiME will be apparently reset
and sends a carriage return (0x0d) with 9600Baud.
Until <64kBytes the DigiME stays silent, like expected.
This disturbes the currently active communication with any of the other interfaces.
My hope is, there are any software/firmware workaounds rather than redesign the hardware…
Again, the other serial interfaces works as expected. The serial out stays at logical 1, if not serviced, but DigiME only till 64kByte has been sent.
Thanks in advance for any hint,