Unfortunately this 3CREVF100-73 firewall became relatively quickly EOL after the acquisition of 3Com by HP.
Therefore, there will be most likely NO feature updates. Also security updates are no planed. (This may be the worst disadvantage.) All in all, this firewall series did not have a very long lifetime. It seems that HP has no big interests in small business firewall products.
I play some time with these (3Com specific) VLAN parameters within my 3CREVF100-73 firewall, - but I have no solution / workaround for you. I had only the problem that the firewall address is accessible on all VLANs when entering it manually in the browser. That should not be so…
However, the only way to gain more features would be an alternative firmware. Well, because this device is not very common, - it is not supported by the most alternative router / firewall firmware projects.
You can ask HP to make public the source code of this EOL firewall, - then some skilled geeks would be able to add “Inter VLAN routing” and IPv6 support (my preferred option). ;)