Bluetooth packets stuck/delayed


I am using an Arduino Uno R3 board and a Bluetooth shield (itead v. 2.2) which is connected via Bluetooth to another device (I tested Android and WIndows machines). The communication protocol used for sending data over Bluetooth uses 6 bytes (=header+payload+crc) for each payload.

Now my problem is that data sent from the Arduino seems to be stuck, e.g. I have to send more dummy data after the actual payload until the target device receives the payload.

Is there a minimum packet size causing this? How can I send data without addional "useless" payload?