o Fixed a bug which caused Nmap to infer an improper distance against

some hosts when performaing OS detection against a group whose
  distance varies between members. [David, Fyodor]

CHANGELOG

@@ -1,5 +1,9 @@
 # Nmap Changelog ($Id$); -*-text-*-
 
+o Fixed a bug which caused Nmap to infer an improper distance against
+  some hosts when performaing OS detection against a group whose
+  distance varies between members. [David, Fyodor]
+
 o Added a new NSE OpenSSL library with functions for multiprecision
   integer arithmetics, hashing, HMAC, symmetric encryption and symmetric
   decryption. [Sven]

osscan2.cc

@@ -3659,7 +3659,7 @@ static void endRound(OsScanInfo *OSI, HostOsScan *HOS, int roundNum) {
 
   for(hostI = OSI->incompleteHosts.begin(); 
       hostI != OSI->incompleteHosts.end(); hostI++) {
-
+    distance = -1;
     hsi = *hostI;
     HOS->makeFP(hsi->hss);