Working with a ZQ521

from both USB and Bluetooth I'm sending this ZPL string : 

^XA^FO50,50^GB407,204,2^FS^FO100,100^FDThis is a 2.25x1.25 label^FS^FO100,150^FD203 DPI Printer^FS^XZ

however, when sending over Bluetooth the printer produces 5 blank labels and prints one, however over USB is functions as expected (prints one label)

Bluetooth code is very simple : 

Connection thePrinterConn = null;
try
{
   thePrinterConn = new MultichannelBluetoothConnection(theBtMacAddress);
   thePrinterConn.Open();
   thePrinterConn.Write(Encoding.UTF8.GetBytes(ZPLData));
}
catch (Exception e)
{

}