Steps to Reproduce

See fiddle:
http://zkfiddle.org/sample/26euevb/1-ListboxCeRod
Put a breakpoint in Listbox.service() here:
https://github.com/zkoss/zk/blob/master/zul/src/org/zkoss/zul/Listbox.java

Actual Result

The _preloadsz value used to control the number of rendered items is default (50) or the value set by .setPreloadSize(value) in java or preloadSize="value" in zul (both deprecated)
The library property is only used for EE Rod
https://www.zkoss.org/wiki/ZK_Configuration_Reference/zk.xml/The_Library_Properties/org.zkoss.zul.listbox.preloadSize

Expected Result

The library property should affect the preloadsz, and take priority over the deprecated methods

Debug Info

the int preloadSize() method already provide the expected calculation, but is only used for EE Rod:
https://github.com/zkoss/zk/blob/master/zul/src/org/zkoss/zul/Listbox.java#L3508
https://github.com/zkoss/zk/blob/master/zul/src/org/zkoss/zul/Listbox.java#L3430

Root Cause

Workaround

Use .setPreloadSize() or <listbox preloadSize=""/> instead