Deduplicate IPs when merging multiple groups in export

router/route-web-api.py

@@ -1526,9 +1526,13 @@ class RouteHandler(http.server.BaseHTTPRequestHandler):
             return
 
         def _flatten(col):
+            seen = set()
             out = []
             for ips in col.values():
-                out.extend(ips)
+                for ip in ips:
+                    if ip not in seen:
+                        seen.add(ip)
+                        out.append(ip)
             return out
 
         if fmt == "mikrotik" and proto == "all":