JSF: p:fileUpload requiredmessage is apearing on click of another button

Question

I am supporting an old application. This is my first JSF project. I added a new upload functionality. In this page/screem already code was ther to search and download to Excel.

After I added upload functionality, the upload works as expected. But the existing functionality broken. That means when user does a filter/search and click on Export To Excel button, it shows error message that is inside requiredMessage="Select a file to upload..."

No clue why it is happening.

Code:

<p:fieldset id="uploadMonthlyActualVolumeFieldSet" style="width: 80%;height:100% !important" legend="Upload Monthly Data" >
                    <h:panelGrid columns="2" cellpadding="5" styleClass="searchTable"
                        style="width: 60%;margin: 0 auto;">
                        <p:outputLabel value="Select file to upload123" />
                        <p:fileUpload id="uploadFileData"
                            value="#{myBean.m_fileActualVolFile}" mode="simple"
                            skinSimple="true" style="width:80px;" widgetVar="uploadFileData"
                            allowTypes="/(\.|\/)(csv)$/" required="false"
                            requiredMessage="Select a file to upload..." />
                    </h:panelGrid>

                    <h:panelGrid style="margin-top: 10px" columns="1" styleClass="buttonGridStyle">
                        <h:panelGroup>
                            <p:commandButton value="Upload" id="uploadBtn"
                                onclick="PF('confirmDialog').show();"
                                ajax="true" global="true" />
                            <p:commandButton value="Cancel" id="cancelBtn"
                                action="#{myBean.cancelImport()}"
                                immediate="true" />
                            <div style="display: none">
                                <p:commandButton id="hiddenUpload" value="Import File Hidden"
                                    onclick="PF('pbAjax').start();"
                                    action="#{myBean.uploadMonthlyClicked}" ajax="false" />
                                <p:commandButton value="Start" id="startProBar" type="button"
                                    onclick="start()" ajax="false" update="progressBarClient"
                                    widgetVar="startButton1" />
                            </div>
                            <center style="margin-top: 15px">
                                <p:progressBar widgetVar="pbAjax" ajax="true" global="false"
                                    value="#{myBean.progress}"
                                    labelTemplate="{value}%" styleClass="animated"
                                    style="width:300px">
                                </p:progressBar>
                            </center>
                        </h:panelGroup>
                    </h:panelGrid>
                </p:fieldset>

<h:panelGrid columns="1" cellpadding="5" style="margin: 0 auto;">
            <p:commandButton id="exportToExcel123" value="Export To Excel" 
                action="#{myBean.exportToExcel}"
                update="messages" ajax="false" global="false"
                rendered="#{myBean.viewMyDVO.m_strProductionvolumeType eq 'AU' ||
                myBean.viewMyDVO.m_strProductionvolumeType eq 'BU' }">
            </p:commandButton>
    </h:panelGrid>