1. Create a Seam Web Project.
2. Open .project
3. Re-place WST validation builder before KB builder:

<buildCommand>
    <name>org.eclipse.wst.validation.validationbuilder</name>
        <arguments>
	</arguments>
</buildCommand>
<buildCommand>
    <name>org.jboss.tools.jst.web.kb.kbbuilder</name>
        <arguments>
        </arguments>
</buildCommand>

4. Save the file.
5. See problems view. Here is an error about incorrect builder order.
6. Invoke the corresponding quick fix (see pop up menu for the error) to re-order the builders.
7. Sometimes Eclipse hangs here.