Problem is in the following code of MessagePackUnpacker.java

...
       case 0xd9: // str 8
        {
              int count = in.getByte();
...

byte is a signed type!
If string length > 127, then count will be negative number, so tryReferRawBody will be called with second parameter as negative number.

...
            if (!tryReferRawBody(a, count)) {

...

Thus we will get java.lang.IllegalArgumentException: Bad limit (capacity 1024): -65 expection