Per random(4) manpage, on kernel 2.6, /proc/sys/kernel/random/poolsize is a read-only file giving the size of the pool in _bits_. It also says "it contains the value 4096", seemingly implying that this is globally true, so why should we read from the file at all?
On the other hand, the same manpage advertises the practice of reading the pool size from that file, and using it as a _byte_ count for dd, which is exactly what rc.shutdown does.

We have bad documentation and resulting bad practice at hand.

Assuming that this value of 4096 still can change along with kernel versions and perhaps compilation options or similar, reading the value from the file (which we already do) and dividing it by 8 (which we don't do) would probably be the best solution.

So slap a ((POOL_SIZE /= 8)) onto there after the 'read POOL_SIZE'.