Created Unassigned: corrupt XLSX file after reference (formlua) to a CellValue, which contains a "&" sign [13893]

I am using:

- Visual Studio 2012 Pro. Patch 5
- MS Office 2010 Ent. SP2 and last patches
- NPOI version 2.1.3.1 via NuGet

How to reproduce:

1. Create a XLSX file with Office 2010 with a CellValue("&") in maybe cell A1 on first sheet
2. Add a formula on the seconde sheet in A1 what is a reference of A1 on the first sheet
3. save the file

4. Open file with NPOI as IWorksheet don't edit it
5. save it

Result is a corrupt XLSX, what you cannot open with MS Excel.
If you repait it, i will remove the reference (formula) on the second sheet.

I can open a file with MS Office 2010, which does not contains a "&" sign without problems!
The file is corrupt if there is a reference to a value with a "&" sign, without reference and "&" ... no problem to open it.