Primefaces selectOneMenu component items not rendered in separate file using ui:include

Question

I one of my Primefaces faces projects I've created a complex form (main.xhtml) with one large panel (used for advanced filter) which I show on-demand. It worked perfectly.

Later I decide to do some xhtml refactoring and I've moved the filter panel from main form (main.xhtml):

<ui:include src="/views/filter.xhtml"/>

to separate form (filter.xhtml):

<ui:composition xmlns="http://www.w3.org/1999/xhtml"
    xmlns:f="http://xmlns.jcp.org/jsf/core"
    xmlns:h="http://xmlns.jcp.org/jsf/html"
    xmlns:p="http://primefaces.org/ui"
    xmlns:pe="http://primefaces.org/ui/extensions"
    xmlns:ui="http://xmlns.jcp.org/jsf/facelets" >
...
    <p:selectOneMenu id="filterSignature"
            value="#{filter.signature}" autoWidth="true"
            style="width:200px; vertical-align:middle;">
        <p:ajax event="change" process="@this" />

        <f:selectItem itemValue="#{null}" itemLabel="" />
        <f:selectItem itemValue="da" itemLabel="Da" />
        <f:selectItem itemValue="ne" itemLabel="Ne" />                  
    </p:selectOneMenu>

...
</ui:composition>

After refactoring components renders fine but all drop down components (such as p:selectOneMenu or p:selectCheckboxMenu) remains empty without any dropdown data no matter if I'm using f:selectItem or f:selectItems.