Nmap-4.20 hitting retrans cap and stalling

[Peter Erickson <perickson () redlamb net>]

I have been trying to conduct a port scan on a locally connect machine  
using Nmap 4.20 and FreeBSD 6.2-Stable. Upon running the scan, I  
immediately begin to receive errors stating that nmap is "Increasing  
the send delay for w.x.y.z from 0 to 5 due to 11 out of 31 dropped  
probes since last increase". After a few more increases I then see the  
same message, but this time due to max_successful_tryno. After letting  
nmap run a bit longer, I receive the following:

SYN Stealth Scan Timing: About 3.66% done; ETC: 21:46 (0:13:12 remaining)
Warning: Giving up on port early because retransmission cap hit.

And nmap hangs... or at least appears to hang. Eventually I'll receive  
another timing message which usually indicates that it will take  
longer than previously expect. I get this same error when running a  
portscan against 127.0.0.1.

I originally thought that this was an issue with FreeBSD, but just  
realized that running the same scan (nmap -A -vv -P0 w.x.y.z) using  
nmap 4.11 produces a final result within 34 seconds.

I'm not 100% sure that this is a bug with nmap, but if this is a bug I  
am willing to help out to solve the problem... I'm not quite sure my  
programming abilities are good enough to fix this on my own, but am  
willing to try with some guidance.

If this is not a bug, any assistance with solving this issue would be  
greatly appreciated. Thanks in advance.

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