Steps to Reproduce

1. Run the attached file.
2. Open the first panel.

Current Result

A regression bug of https://sourceforge.net/p/zk1/bugs/2114/

Expected Result

No regression.

Debug Information

Only in Panel w/ client ROD + Vertical Tabbox

Since the initial state of Tabbox is invisible, onSize won't be executed.
https://github.com/zkoss/zk/blob/v8.6.1/zul/src/archive/web/js/zul/tab/Tabs.js#L42

The .z-tabs-content CSS height: 4096px would make height big if the outer height z-tabs isn't restricted.

A selected tab will trigger _fixWidth, but the timing is afterMount which is executed in the next tick.
https://github.com/zkoss/zk/blob/v8.6.1/zul/src/archive/web/js/zul/tab/Tab.js#L266

Workaround

Disable Panel client rod

<custom-attributes org.zkoss.zul.client.rod="false"/>