Attempt stacking 'CAN-BUS' and 'USB Host' Shields on Mega 2560 I've run into a case of 'In theory it works, but in reality'....

I'm using the CAN-BUS Shield V1.2 from Seeed studio. Many things are written in broken english, so I'm starting to wonder if I can trust all of the information. http://wiki.seeed.cc/CAN-BUS_Shield_V1.2/

The USB Host Shield is a discontinued official Arduino model. https://www.arduino.cc/en/Main/ArduinoUSBHostShield

(I would link to the libraries, but I am unable to post more than 2 links)

CAN-BUS Pins:

AREF
ICSP (SCK, MISO, MOSI)
P9 - CS (SS)
P2 - INT
NC
IOREF
RST
3.3V
5V
Vin


USB Host Pins:

ICSP (SCK, MISO, MOSI)
P10 - SS
P7 - GPX
P8 - INT (actually RES?)
P9 - RES (actually INT?)


The only conflict I see is Pin 9 (CS on CAN, RES on USB). This is where it gets hazy... While the documentation on the bottom of the USBHost page implies that Pin 9 is RES, in the code Pin 9 is actually INT.

So, assuming Pin 9 is actually INT, I re-routed it to Pin 45 on on the Mega and changed it in the UsbCore.h file:

//typedef MAX3421e&lt;P10, P9&gt; MAX3421E; // old
typedef MAX3421e&lt;P10, P45&gt; MAX3421E; // new


Here is a snippet of the code I am running:

#include &lt;PS3BT.h&gt;
#include &lt;usbhub.h&gt;

#ifdef dobogusinclude
#include &lt;spi4teensy3.h&gt;
#include &lt;SPI.h&gt;
#endif

#include &lt;Bounce2.h&gt;
#include &lt;Time.h&gt;
#include &lt;TimeLib.h&gt;
#include &lt;SPI.h&gt;
#include "mcp_can.h"

const int SPI_CS_PIN = 9;

MCP_CAN CAN(SPI_CS_PIN); // Set CS pin

void setup()
{
    Serial.begin(115200);

    // THIS WORKS
    if (Usb.Init() == -1) {
        Serial.print(F("\r\nOSC did not start"));
    }
    Serial.print(F("\r\nPS3 Bluetooth Library Started"));

    // THIS FAILS
    while (CAN_OK != CAN.begin(CAN_500KBPS))
    {
        Serial.println("CAN BUS Shield init fail");
        Serial.println(" Init CAN BUS Shield again");
        delay(100);
    }
    Serial.println("CAN BUS Shield init ok!");
}


The CAN-BUS Fails to init until I physically remove the USB Host Shield. 

If I remove the CAN-BUS code, The USB Host Shield functions normally. 

If I remove the USB Host code, the CAN-BUS Shield still DOES NOT init.

I tried to sift through the CAN-BUS init code a little, and I can only assume it's failing to communicate via SPI. What am I missing here?
I think that there is an hardware bug on the USB Master shield:
IC3, the 3-state buffer which converts MISO to 5V, is always active...
The enable pin of this 74LVC1G125 (pin 1) should be connected to the pin ss_3V3.
Then you can stack this shield with another one.