checker: Ensure a flag is found before considering a good response

libfic/exercice.go

@@ -594,8 +594,11 @@ func (e *Exercice) CheckResponse(cksum []byte, respflags map[int]string, respmcq
 					valid = valid && flag.IsOptionnal()
 				}
 			} else {
-				flag.FoundBy(t)
-				goodResponses += 1
+				err := flag.FoundBy(t)
+				if err == nil {
+					// err is unicity issue, probably flag already found
+					goodResponses += 1
+				}
 			}
 		}