class Product {
static hasMany = [features:ProductFeature, projects:Project, sprints:Sprint, issues:Issue, tasks:Task, attachments:Attachment, notes:Note, links:Hyperlink]
String productName
String productKey
...... other attribs
}

class Project {
static hasMany = [tasks:Task, issues:Issue, features:ProductFeature, teamMembers:User, attachments:Attachment, notes:Note, links:Hyperlink]
static belongsTo = [Product]
static optionals = ['productVersion']

Product product
...... other attribs
}
class Sprint extends Project {
//Inherited relationships:
// static hasMany = [tasks:Task, issues:Issue, teamMembers:User, attachments:Attachment, notes:Note, links:Hyperlink]
// static belongsTo = [Product]

Integer sprintNumber
}

When a new product is created using scaffold pages. It can be updated again using scaffold pages. Everything works as intended. Now when we setup sprint and project for a product, Now product can not be updated anymore because of following exception.
org.codehaus.groovy.runtime.InvokerInvocationException: org.hibernate.WrongClassException: Object with id: 1 was not of the specified subclass: Sprint (loaded object was of wrong class class Project)
at org.codehaus.groovy.runtime.metaclass.ReflectionMetaMethod.invoke(ReflectionMetaMethod.java:64)
at org.codehaus.groovy.runtime.MetaClassHelper.doMethodInvoke(MetaClassHelper.java:678)
at groovy.lang.MetaClassImpl.invokeMethod(MetaClassImpl.java:689)
at groovy.lang.ExpandoMetaClass.invokeMethod(ExpandoMetaClass.java:894)
at groovy.lang.MetaClassImpl.invokeMethod(MetaClassImpl.java:531)
at groovy.lang.Closure.call(Closure.java:290)
at groovy.lang.Closure.call(Closure.java:285)
at org.codehaus.groovy.grails.web.servlet.mvc.SimpleGrailsControllerHelper.handleAction(SimpleGrailsControllerHelper.java:526)
at org.codehaus.groovy.grails.web.servlet.mvc.SimpleGrailsControllerHelper.executeAction(SimpleGrailsControllerHelper.java:385)
at org.codehaus.groovy.grails.web.servlet.mvc.SimpleGrailsControllerHelper.handleURI(SimpleGrailsControllerHelper.java:240)
at org.codehaus.groovy.grails.web.servlet.mvc.SimpleGrailsControllerHelper.handleURI(SimpleGrailsControllerHelper.java:152)
at org.codehaus.groovy.grails.web.servlet.mvc.SimpleGrailsController.handleRequest(SimpleGrailsController.java:88)
at org.springframework.web.servlet.mvc.SimpleControllerHandlerAdapter.handle(SimpleControllerHandlerAdapter.java:45)
at org.codehaus.groovy.grails.web.servlet.GrailsDispatcherServlet.doDispatch(GrailsDispatcherServlet.java:241)
at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:755)

Note sure weather there is something wrong this inheritance relationship. If I remove inheritance relationship between project and sprint, everything works as intended. Please advice.