steps to reproduce

1. run the attached zul with a blank file under 3.8.3.RC
2. click "create" button to create a sheet
3. click "delete" to delete the newly created sheet

result

SEVERE:
java.lang.IllegalStateException: doesn't connect to parent
at org.zkoss.zss.model.impl.SheetImpl.checkOrphan(SheetImpl.java:1446)
at org.zkoss.zss.model.impl.SheetImpl.getBook(SheetImpl.java:150)
at org.zkoss.zss.range.impl.NotifyChangeHelper.notifyMergeSync(NotifyChangeHelper.java:127)
at org.zkoss.zss.model.impl.BookImpl.sendModelEvent(BookImpl.java:232)
at org.zkoss.zss.range.impl.NotifyChangeHelper.notifySheetDelete(NotifyChangeHelper.java:182)
at org.zkoss.zss.range.impl.RangeImpl$33.doBeforeNotify(RangeImpl.java:1314)
at org.zkoss.zss.range.impl.RangeImpl$ModelManipulationTask.invoke(RangeImpl.java:1743)
at org.zkoss.zss.model.util.ReadWriteTask.doInWriteLock(ReadWriteTask.java:43)
at org.zkoss.zss.range.impl.RangeImpl.deleteSheet(RangeImpl.java:1317)
at org.zkoss.zss.api.impl.RangeImpl.deleteSheet(RangeImpl.java:691)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)

debug info

• it doesn't happen in 3.8.2
• the newly created sheet contains an unsynchronized merged cell which is created by setAutoRefresh(false).

workaround

• Notify the change for the sheet before deleting.