In https://github.com/vyos/vyos-1x/pull/1152 a change was introduced to the way port validation works.
It does this by implemeting the Python range function to check if the specified port is within a specific range. However, the Python range function is defined as follows:
boundary value up to which (excluding this value) the range or sequence is to be returned
This means that if you define a firewall rule with a port range with an upper port of 65535, the validation will fail, because currently the highest allowed port is actually 65534.