Firewall Mangle - Mark Routing - getting error after 255 have been entered

It seems that I cannot enter more than 255 mark routing entries, mark packet no problem, but any over qty 256 are displaying a “bad new routing mark” in red.

(V6.29.1 on a CCR)

Anyone seen this before and or have a work around?

To update the post, I have spoken with support and they agree with my findings and it won’t change until v7.