Several IComponentResolvers (like InlineEnclosureHandler and WicketMessageTagHandler) create dynamic Component id from the ComponentTag id + page.getAutoIndex() only if the respective IComponentResolver recognize the ComponentTag id.
This should be improved and should set the auto index if the ComponentTag id has a predefined namespace.
WICKET-4520. There a ComponentTag looks like <div wicket:enclosure=... wicket:message=...> and thus both IMarkupFilters manipulate the ComponentTag but just the first one sets its id. Later InlineEnclosureHandler acting as IComponentResolver sees 'wicket_message' as tag id and decides to not add the auto index.