Page lastModified property

Hi all, on our project we are using maven vault plugin for deploying application on AEM and I've found something like an issue. After deploying content there are no cq:lastModified and jcr:lastModified properties under jcr:content node (cq:PageContent) but if try to create page through the siteadmin or just modify page these properties exist. Is it a normal behaviour or any ideas why it happens?

Thanks.