Maybe it will find its way in the coming Version.
I guess the PWM for pin44 was forgotten in the actual release. if you add:
} else if (digitalPinToTimer(pin) == TIMER5C) {
// connect pwm to pin on timer 5, channel B
sbi(TCCR5A, COM5C1);
// set pwm duty
OCR5C = val;
to the wiring_analog.c the PWM will be executed on pin44.
if you know any other reason (except being forgotten) why it wasn't implemented, please let me know.