popup loading overlay in wrong position

Steps to Reproduce

run the snippet:

<zk>
 <menupopup id="menu" onOpen="if (event.isOpen()) Thread.sleep(1000)">
    <menuitem label="Item 1" />
    <menuitem label="Item 2" />
    <menuitem label="Item 3" />
 </menupopup>
 <div width="300px" height="300px" style="border: 1px solid black" context="menu" />
</zk>

right click inside the area to trigger a popup
repeat this and observe the loading overlay position

Current Result

loading overlay displays outside the popup (at the previous popup position)

Expected Result

loading animation positioned correctly inside the popup

Debug Info

this used to work in 8.0.5

Workaround