value of a container option (e.g. array) is reset to empty on first specification

opt-base.go

@@ -13,6 +13,7 @@ type cliOptionBase struct {
 	description      string
 	isArray          bool
 	hidden           bool
+	alreadySeen      bool
 	specialValues    map[string]SpecialValueFunc
 	incompatibleWith []string
 }