Okay, I've taken a good, hard look at this one. Sorry it has taken so long to get to it. This bug has exposed quite a few problems in the hex converter, which will be difficult to resolve in old releases. I am researching options to resolve this issue, but a fix will not be available anytime soon.
The bug does not occur if you use --romwidth=8 --memwidth=8. (You would have to alter the romwidth directive in the ROM specification, or remove it). This is the recommended mode for operating the hex converter on C6000. Is this an acceptable workaround?