F2810 CANBUS register write corruption.

	msgid_buf = 1234UL;
Hi,
I'm having issues writing to the MSGID field of the CANBUS controller. 
Specifically, the value I read from the MSGID.all field comes out as a different value every time no matter what I write to it.
Other MBOXes work fine. I have tried this with, and without the "shadow" register, although example code from the SPRA876a document does not use the shadow register.
The code below produces this output: 
(Canbus init is not shown, and other mailboxes work (confirmed with another device on the RX end))

MSGID_BUF: 0x000004D2
MSGID: 0x0D0B8801

The value displayed for MSGID changes every time.



	puts("MSGID_BUF: ");
	putxxxx(msgid_buf);
	puts("\n");


	struct MBOX shadow_mbox = ECanaMboxes.MBOX0;
	shadow_mbox.MSGID.all = msgid_buf;

	ECanaMboxes.MBOX0 = shadow_mbox;

	puts("MSGID: ");
	putxxxx(ECanaMboxes.MBOX0.MSGID.all);