WRT54GC - some ports can't be blocked

Hi

I am trying to set up a comprehensive port block for everything above
443, but some port number ranges are refused for no obvious reason.

Anything above about 32000 (possibly 32767) is accepted but there
seems to be a bug in that the number is displayed as zero, so e.g.

6000-40000

is displayed as

6000-0

Then, some port ranges just below 5300 cannot be set, and I can't see
why. I can set a block of 5300-32000 but anything between 444 and 5300
seems to be refused.

Can anybody suggest why? I have been around all the remaining config
of the router and can't see anything.

Below 443 it seems to be OK.

One can set a max of 2 blocks oer policy but I've noticed one can have
multiple policies, each specifying a particular MAC number or range,
so in effect one can get past the "2 exclusions max" limit.