--annotate) annotate="$1"; shift ;;
                --no-annotate) annotate= ;;
                -b) branch="$1"; shift ;;
-               -P) prefix="$1"; shift ;;
+               -P) prefix="${1%/}"; shift ;;
                -m) message="$1"; shift ;;
                --no-prefix) prefix= ;;
                --onto) onto="$1"; shift ;;
                        p="$p -p $parent"
                fi
        done
-       
-       if [ -n "$identical" ]; then
+
+       copycommit=
+       if [ -n "$identical" ] && [ -n "$nonidentical" ]; then
+               extras=$(git rev-list --count $identical..$nonidentical)
+               if [ "$extras" -ne 0 ]; then
+                       # we need to preserve history along the other branch
+                       copycommit=1
+               fi
+       fi
+       if [ -n "$identical" ] && [ -z "$copycommit" ]; then
                echo $identical
        else
                copy_commit $rev $tree "$p" || exit $?