How to fix p:selectOneMenu result item lists moves as when mouse scrolls and not stick to selectOnMenu box - primefaces

Question

p:selectOneMenu result itemlists are initially shows stick to selectOneMenu dropdown, As when I scroll using mouse scroller the result Itemlist moves up or down as I scroll the mouse.
This p:selectOneMenu I have in the dialog box.
This works fine if I use the h:selectOneMenu. The problem is in p:selectOneMenu (primeface 6.2 version).
I have tried with attribute PanelStyle="position:fixed;" but this not helped. The problem appears only in when I use mouse scroller.
Can somebody please guide me how to fix this.
<p:dialog header="Add User" widgetVar="addUserWidget" id="addUserWidgetId" modal="true">
<p:fragment>
<h:panelGrid columns="2" id="myGridPanelId" width="180px">
<h:panelGroup id="groupPan">
<p:selectOneMenu value="#{myBean.selectedUser}" style="width:140px;">
<f:selectItems
value="#{myBean.userLists}" id="userNameItem"
var="user" itemLabel="#{user.name}" itemValue="#{user.name}">
</f:selectItems>
<f:ajax event="change" execute="#this" render="groupPan" listener="#{myBean.userAdd()}" />
</p:selectOneMenu>
</h:panelGroup>
</h:panelGrid>
<h:panelGrid id="panelBtnGrid">
<p:commandButton ajax="true" value="Add" id="addBtnId" process="#this"
action="#{myBean.saveUser()}" />
</h:panelGrid>
</p:fragment>
</p:dialog>
The result Item list should stick to the p:selectOneMenu dropdown box.