Reproducing Steps:

1. run with attached zul and composer
2. scroll the bar to the right
   
3. switch to next page

Actual:

An JS error is showed.
無法處理：
setAttr
Cannot read property 'cells' of undefined (TypeError)

JS stack trace:

Uncaught TypeError: Cannot read property 'cells' of undefined zul.mesh.wpd:3230
zul.mesh.Frozen.zk.$extends._doScrollNow zul.mesh.wpd:3230
zul.grid.Grid.zk.$extends.refreshBar_ zul.grid.wpd:382
zk.override.setResetDataLoader zk.wpd:28279
zk.copy._set2 zk.wpd:10268
zk.Widget.zk.$extends.set zk.wpd:15373
zAu.cmd1.setAttr zk.wpd:19963
doProcess zk.wpd:19032
doCmdsNow zk.wpd:19273
zAu._doCmds zk.wpd:19513
afterResponse zk.wpd:19164
onResponseReady

Expected:

switch to next page and no JS error shows.

Workaround:

Set the property below and this issue doesn't appear.

<library-property>
    <name>org.zkoss.zul.nativebar</name>
    <value>true</value>
</library-property>

Customer's Comment

Customer said: "code for columns creation in paging() of PagingComposer.java was redundant code and it didn't necessary to business logic". That means creating Columns when onPaging event happens is not their real requirement. After the user remove those codes, the issue disappear.