To reproduce:
Create Quiz.
Add multiple choice question.
Set it as multiple correct answers.
Fill in several answers (I used four).
Set *all* answers to be correct.
Save.

Exception thrown:

org.sakaiproject.portal.api.PortalHandlerException:
org.sakaiproject.tool.api.ToolException: 4
    at
org.sakaiproject.portal.charon.handlers.ToolHandler.doPost(ToolHandler.java:63)
caused by: org.sakaiproject.tool.api.ToolException: 4
    at
org.sakaiproject.portal.charon.SkinnableCharonPortal.forwardTool(SkinnableCharonPortal.java:1099)
caused by: javax.servlet.ServletException: 4
    at
org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:269)
caused by: java.lang.ArrayIndexOutOfBoundsException: 4
    at
org.sakaiproject.tool.assessment.ui.listener.author.ItemAddListener.checkMC(ItemAddListener.java:266)
    at
org.sakaiproject.tool.assessment.ui.listener.author.ItemAddListener.processAction(ItemAddListener.java:117)
    at javax.faces.event.ActionEvent.processListener(ActionEvent.java:57)
    at javax.faces.component.UIComponentBase.broadcast(UIComponentBase.java:649)
    at javax.faces.component.UICommand.broadcast(UICommand.java:297)
    at javax.faces.component.UIViewRoot.broadcastEvents(UIViewRoot.java:267)
    at javax.faces.component.UIViewRoot.processApplication(UIViewRoot.java:381)
    at
com.sun.faces.lifecycle.InvokeApplicationPhase.execute(InvokeApplicationPhase.java:75)
...