You might try modifying a standard sort/merge operation. A brief pseudocode description is:

SortByBugID("BugDescriptions","BugDescriptions.s");
SortByBugID("BugComments","BugComments.s");
BD = open "<BugDescriptions.s"
COM = open "<BugComments.s"
OUT = open ">ResultFile"

curBD = <BD>
curCOM = <COM>

while !BD.eof && !COM.eof {
   if curBD.BugID < curCOM.BugID {
      write OUT, curBD
      curBD = <BD>
   }
   elsif curBD.BugID == curCOM.BugID {
      curBD.Comment .= curCOM.Comment
      curCOM = <COM>
   }
   else {
      die "Missing bug description?"
   }
}
[download]

If you're interested in this method, I have an earlier node with working code for a similar problem.