Not presenting expected errors

[Heucles]

When addged soap envelope, it stopped showing errors such as data type validation and invalid tags name or tags missing.
What I did was, added this tag :
<xs:import namespace="http://schemas.xmlsoap.org/soap/envelope/" schemaLocation="soap-envelope.xsd"/>
at the ".xsd" file and then is stoped presenting errors to me, is this a known berraviour?