Steps to reproduce

1. load attached file

Actual result

org.zkoss.zss.model.InvalidModelOpException: the region is overlapped A1:D1[0,0,0,3]:A1:D1[0,0,0,3]
at org.zkoss.zss.model.impl.SheetImpl.addMergedRegion(SheetImpl.java:1588)
at org.zkoss.zss.range.impl.imexp.AbstractExcelImporter.importMergedRegions(AbstractExcelImporter.java:397)
at org.zkoss.zss.range.impl.imexp.AbstractExcelImporter.imports(AbstractExcelImporter.java:157)
at org.zkoss.zss.range.impl.imexp.ExcelImportAdapter.imports(ExcelImportAdapter.java:46)
at org.zkoss.zss.range.impl.imexp.AbstractImporter.imports(AbstractImporter.java:54)
at org.zkoss.zss.ui.Spreadsheet.getSBook(Spreadsheet.java:647)
at org.zkoss.zss.ui.Spreadsheet.getSelectedSSheet(Spreadsheet.java:845)
at org.zkoss.zss.ui.Spreadsheet.doInvalidate(Spreadsheet.java:4668)
at org.zkoss.zss.ui.Spreadsheet.invalidate(Spreadsheet.java:4007)
at org.zkoss.zss.ui.Spreadsheet.setSrc(Spreadsheet.java:885)

workaround

<spreadsheet 
  importer="${c:new('foo.PatchedImporterImpl')}"/>