Created Unassigned: Exception opening a file in read-only mode [13397]

If I open an xlsx file with
```
workBook = new XSSFWorkbook(OPCPackage.Open(path,PackageAccess.READ));
```
it later throws an exception
```
NPOI.POIXMLException
en NPOI.POIXMLDocumentPart.CreateRelationship(POIXMLRelation descriptor, POIXMLFactory factory, Int32 idx, Boolean noRelation)
en NPOI.POIXMLDocumentPart.CreateRelationship(POIXMLRelation descriptor, POIXMLFactory factory)
en NPOI.XSSF.UserModel.XSSFWorkbook.OnDocumentRead()
en NPOI.POIXMLDocument.Load(POIXMLFactory factory)
en NPOI.XSSF.UserModel.XSSFWorkbook..ctor(OPCPackage pkg)
```
containing
```
System.InvalidOperationException "Operation not allowed, document open in read only mode!"
en NPOI.OpenXml4Net.OPC.OPCPackage.ThrowExceptionIfReadOnly()
en NPOI.OpenXml4Net.OPC.OPCPackage.CreatePart(PackagePartName partName, String contentType, Boolean loadRelationships)
en NPOI.OpenXml4Net.OPC.OPCPackage.CreatePart(PackagePartName partName, String contentType)
en NPOI.POIXMLDocumentPart.CreateRelationship(POIXMLRelation descriptor, POIXMLFactory factory, Int32 idx, Boolean noRelation)
```
It works if I use read&write PackageAccess.
Doesn't NPOI allow to simply read the file?