JSF: commandLink works in my environment but not in my partner's environment

Using JSF as shown:

<h:commandLink action="#{bean.goBack()}"><img src=... /></h:commandLink>

it works fine in my dev environment and redirects me to the page provided by the bean.

But it doesn't work in my peers' development environment. It only makes a refresh of the page. By placing a BreakPoint I can see that the page never calls the goBack method.

But including the immediate option as shown:

<h:commandLink immediate="true" action="#{bean.goBack()}"><img src="... /></h:commandLink>

it works fine in my peers' development environment.

We use Eclipse. Each of us has a JBOSS 6.1 server in our own environment.

What configuration is allowing me to run commandLink without adding immediate?