pf behaviour with tcp ports 439 and

Is there any reason why pf might behave in a special way for tcp ports 
439 & 445?  I just happened to notice that with a minimal pf.conf:

# macros
ext_if="pppoe0"
int_if="ep2"

# nat/rdr
nat on $ext_if from !($ext_if) -> ($ext_if:0)

# filter rules
block in log
pass out log
pass in log quick on $int_if

No matter how hard I look I NEVER see a blocked or passed packet in the 
log file for incoming packets to ext_if for tcp ports 439 & 445.  Every 
other port behaves entirely as expected when I test this out.  I first 
became aware of this when playing around with GRC sheilds-up - it listed 
439 & 445 as 'stealth', even when I forced block-policy to 'return'.

I might be missing something blindingly obvious here, but...

Any thoughts?


Thanks
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