Against the issue ICE-9676, it is currenty not possible the clear the input field after pressing a button.
Simple example with facet entry rendering:
<ace:autoCompleteEntry rows="25" listVar="entry" width="800"
id="entryid" reset="#{testCtrl.resetText}" filterMatchMode="none"
style="margin-left: 10px;"
filterBy="#{entry.fieldForFiltering}"
binding="#{testCtrl.autoCompleteEntryBinding}"
value="#{testCtrl.inputTextValue}"
listValue="#{testCtrl.possibleEntries}"
valueChangeListener="#{testCtrl.entrySelected}"
textChangeListener="#{testCtrl.triggerEntryFiltering}">

<f:facet name="row">
<h:panelGrid columns="1" rules="all" width="100%"
columnClasses="autocompleteWidth">
<h:outputText value="#{entry.fieldForFiltering}" />
</h:panelGrid>
</f:facet>
<ace:ajax event="valueChange" render="@all" />

</ace:autoCompleteEntry>

<ace:pushButton actionListener="#{testCtrl.pressButton}" type="button"
styleClass="linkButton">
<ace:ajax render="@all" execute="@form" />
<h:graphicImage value="../resources/img/add_green.png" style="float:right" />
</ace:pushButton>

Content of pressButton:
public void pressButton(ActionEvent event) {
resetText = true;
inputTextValue = null
}