browser inconsistent popup/tooltip behavior

Steps to Reproduce

<zk>
    <button label="popup" width="100px" height="100px"
            popup="pp"
            tooltip="tt,delay=1000"/>

    <button label="popup toggle" width="100px" height="100px"
            popup="pp, type=toggle"
            tooltip="tt,delay=1000"/>

    <popup id="pp">popup content</popup>
    <popup id="tt">tooltip</popup>
</zk>

hover the buttons,
click the button before the tooltip delay of 1sec to open the popup
don't move the mouse after the click

Current Result

chrome: the popup opens
-> tooltip doesn't open (only when moving the mouse away from the popup)

FF/edge/IE11: the popup opens
-> after the delay the tooltop opens as well (closing the popup on the second button)

Expected Result

a consistent behavior, preferably the chrome behavior (opening a popup cancels the tooltip delay)
the tooltip should not cover/close the popup without further user intend (=moving the mouse away from the popup)

Debug Info

Root Cause

1. The popup has border-radius. The mouse pointer might on the popup element or not because of the subpixel.
2. ZK-4525

Workaround

<style><![CDATA[
    .z-popup {
        border-radius: 0;
    }
]]>
</style>