C# – SerialPort timeouts in standalone mode

I have a strange behaviour im my app.

I open a COM port to comunicate witha a device over Bluetooth. I do the following steps:

1. Open the virtual COM port;
2. Switch remote bluetooth to command mode;
3. Perform few commands (eg. read remote device's serial number);
4. Switch remote bluetooth to data amode;
5. Send data to device;

6. Read a byte of answer (ReadByte() from SerialPort class);

   The device works fine and answers immediately and everything is fine while I run my app in debug mode via visual studio.

But when I try to run it directly (without visual studio and adebugger attatched – but still compiled with "Debug" option) i get a timeout exception at step 6.

The bug is fully reproducible (no timeouts in Visual Studio, and every time without it).

Does anyone have any idea that could cause such behaviour ?

Here is the code from step 6

    private byte[] ReadResponse() {

        try {
            int bytes2Read = 6;
            do {
                this.buffer.Append((byte)ReadByte()); // <- there the timeout occurs

                if (this.buffer.Length == 6) { // header receiver
                    // bytes 2 and 3 contain message length
                    bytes2Read = this.buffer[2] + (this.buffer[3] << 8);
                }
            } while (this.buffer.Length < bytes2Read);

            return this.buffer.ToArray();
        } finally {
            this.buffer.Clear();
        }
    }

The method is situated in the class that derives from SerialPort class.