I have the following code (Arduino 1.6.1):

if(_bt.available() > 0) {
 int data = _bt.peek();
 bool found = true;
 if(data == 'a') {
 // do something
 } else if(data == 'b') {
 // do something else
 } else {
 found = false;
 }
 if(found) _bt.read();
}

(It's set up like this because it's a library, and if unknown messages are found they should be passed to the code handling other commands, if that makes sense)

At random points the Arduino would stop reacting to any received messages, and after adding some debug code I found out that while _bt.available() would keep incrementing with each message received, _bt.peek() returns some a nonsense negative value but _bt.read() will return something completely different, these are some i've encountered so far:

-1 == 255
-76 == 180
-1 == 255
-36 == 220
-1 == 255
-5 == 251
-72 == 184
-36 == 220
-18 == 238

I'm not sure where these values originate from because I'm never sending them to the HC-05 attached to this SerialPort. Worth noting is that once this happens even if i disconnect the HC-05 the SoftwareSerial will keep returning the last values, so I assume some buffering is done internally.