RFC3330 issued in September 2002 does indicate that this address block
is subject to future allocations. But I think people were expecting
something from the IAB/IETF before IANA actually allocated previous
special use reserved address blocks. My understanding was RFC3330 was
written by IANA and published by IANA to document existing practices, not
to change previous practices. Eventually we'll use it.
The simpliest solution is for IANA to inform APNIC that it was an
oversight. The 223.255.255.0/24 network block within the 223/8 CIDR block
assigned to APNIC is still IANA-RESERVED per RFC3330 and previous
practice; and not allocated for APNIC's use at this time.
Its probably easier for APNIC to flag the 223.255.255.0/24 network within
the CIDR block 223/8 as IANA-RESERVED in the APNIC database just like
ARIN does with the other IANA-RESERVED blocks in ARIN's database; rather
than do the ugly CIDR block breaking of 223.0.0.0-223.255.254.255 and
223.255.255.0-223-255.255.255. But that is a decision for APNIC.