Two partial responses on the page

Question

please help me. I'm suffering from the situation when I have two partial responses on the page. When I use Tomcat, it's ok, just one response without any additional redirects. It occurs when I use WebSphere application server (WAS 8.5) and try to export to excel:

    <p:commandButton id="export"
                        value="#{msg['button.OK']}"
                        action="#{dataExporter.exportAsXls()}"
                        onclick="PF('exportWarningDialoguePanel').hide();"
                    process="@this" partialSubmit="true"/>

Response (on WAS 8.5) is:

<partial-response id="j_id1">
    <changes><update id="j_idt144:j_idt145"><![CDATA[ bla bla bla]]></update>
    <update id="j_id1:javax.faces.ViewState:0"><![CDATA[e11s1]]/>
</changes>
</partial-response>
<partial-response id="j_id1">
    <redirect url="/app/admin/inbox"></redirect>
</partial-response>

Tomcat's response is:

<partial-response id="j_id1">
    <changes><update id="j_idt144:j_idt145"><![CDATA[ bla bla bla]]></update>
    <update id="j_id1:javax.faces.ViewState:0"><![CDATA[e11s1]]/>
</changes>
</partial-response>

Is it a WAS config issue?