When working on another issue I noticed that a single incoming update was logged on the client as being applied twice. I checked a couple of previous releases and this seems to be the case as far back as BETA2:

ICEfaces 2.1.0.BETA2 (comp-suite.war)
ICEfaces-3.0.0.RC1 (showcase.war)
ICEfaces 3 Trunk (showcase.war)

Using the ACE Showcase (e.g. ace:tooltip, change the effect using the dropdown menu), a single action produces one update and the following logging indicating that the update is applied twice:

[window] applied updates>>
update["j_idt66:tooltipEffectSelector"]:<select id="j_idt66:tooltipEffectSelecto....
update["j_idt66:j_idt96_content"]:<div class="ui-panel-content ui-widget-c....
update["dynamic-code-compat"]:<span id="dynamic-code-compat"></span>....
update["javax.faces.ViewState"]: 641204715261572547:3506558945429355219....

[window] applied updates>>
update["j_idt66:tooltipEffectSelector"]:<select id="j_idt66:tooltipEffectSelecto....
update["j_idt66:j_idt96_content"]:<div class="ui-panel-content ui-widget-c....
update["dynamic-code-compat"]:<span id="dynamic-code-compat"></span>....
update["javax.faces.ViewState"]: 641204715261572547:3506558945429355219....