Export-Excel with Append option generates a large but blank file

[eems-jwimmer]

I have a rather large Excel workbook (23 MB, 174k lines) to which I'm attempting to append additional data from another workbook (3 MB, 24k lines).

Attempting to combine the two using Import-Excel .\NewData.xlsx | Export-Excel .\ExistingData.xlsx -Append results in the ExistingData.xlsx file growing to 25 MB but being completely empty when opened with Excel.

If I run the same command again to effectively double-append the existing file, the following results occur:

• The file grows to 28 MB
• Attempting to open said file in Excel produces an error message: We found a problem with some content in 'ExistingData.xlsx'. Do you want us to try and recover as much as we can? If you trust the source of this workbook, click Yes.
• Clicking yes results in Excel attempting to recover the file, then producing a follow-up message: Repaired Part: /xl/worksheets/sheet.xml part with XML error. HRESULT 0x8000ffff Line 1, column 0.
• The resulting "repaired" workbook is still blank

[dfinke]

need a simple set of data and script to repro the and diagnose