UDP read() doesn't work in conjunction with the Arduino String library

[sstaub]

Following code doesn't work with the Native Ethernet library.
The code works with STM32duino with LWIP and with the WIZNet library

#include "Arduino.h"
#include <TeensyID.h>
#include <NativeEthernet.h>
#include <NativeEthernetUdp.h>

uint8_t mac[6];
IPAddress localIP(10, 101, 1, 201);
IPAddress subnet(255, 255, 0, 0);
uint16_t localPort = 8001;
IPAddress remoteIP(10, 101, 1, 100);
uint16_t remotePort = 8000;

EthernetUDP udp;

void setup() {
	teensyMAC(mac);
	Serial.begin(9600);
	Ethernet.begin(mac, localIP);
	udp.begin(localPort);
	}

void loop() {
	String message;
	int size;
        size = udp.parsePacket();
	if (size > 0) {
		// Fill the msg with all of the available bytes
	                while (size--) {
			message += (char)(udp.read());
			}
                Serial.println(message);
		message = String();
		}
	}

The application stop working when reaching message += (char)(udp.read());
If using the standard C++ string library it works as expected. Also when using a char buffer array.
This example works

#include "Arduino.h"
#include <TeensyID.h>
#include <NativeEthernet.h>
#include <NativeEthernetUdp.h>
#include <string>

using namespace std;

uint8_t mac[6];
IPAddress localIP(10, 101, 1, 201);
IPAddress subnet(255, 255, 0, 0);
uint16_t localPort = 8001;
IPAddress remoteIP(10, 101, 1, 100);
uint16_t remotePort = 8000;

EthernetUDP udp;

void setup() {
	teensyMAC(mac);
	Serial.begin(9600);
	Ethernet.begin(mac, localIP);
	udp.begin(localPort);
	}

void loop() {
	string message;
	int size;
        size = udp.parsePacket();
	if (size > 0) {
		// Fill the msg with all of the available bytes
	                while (size--) {
			message += (char)(udp.read());
			}
                Serial.println(message.c_str());
		message.erase();
		}
	}