Previously this component would submit the contents of its parent form to the server when the designated key was pressed. Now there is still a submit to the server, but none of the fields are sent.

<h:form id="regForm">
  <ace:textEntry id="nameIn" value="#{userBean.name}"/>
  <icecore:defaultAction actionListener="#{userController.register}" key="Enter"/>
</h:form>

In the above case in 3.3 we would see the name being sent to the server, whereas in 4.0 the submit looks like:
f:defaultActionOnEnter=
ice.event.alt=false
ice.event.captured=f:defaultActionOnEnter
ice.event.ctrl=false
ice.event.keycode=13
ice.event.meta=false
ice.event.shift=false
ice.event.target=f:passField_input
ice.event.type=onkeydown
ice.focus=f:passField_input
ice.submit.serialization=element
ice.submit.type=ice.se
ice.view=3i37mg2wl:i6
ice.view=3i37mg2wl:i6
ice.window=c3i37mfmi6
ice.window=c3i37mfmi6
javax.faces.ClientWindow=c3i37mfmi6
javax.faces.ViewState=-8340356029913225045:8446322854127289620
javax.faces.partial.ajax=true
javax.faces.partial.event=keydown
javax.faces.partial.execute=f:defaultActionOnEnter
javax.faces.partial.render=@all
javax.faces.source=f:defaultActionOnEnter
v3i37mg2wl-i6-single-submit=v3i37mg2wl-i6-single-submit

So it's missing something like:

regForm:nameInInput_input