A feature in Excel allows adding ActiveX controls in the Worksheets. You can insert the ActiveX controls from the Developer ribbon tab from the insert button. As it is a missing feature it is not imported and thus removed from the document on export.

The Spilled range operator (#) is responsible for selecting the whole range of values used after a cell reference.

The error is with a message "Index and count must refer to a location within the string (Parameter 'count')" and is thrown inside the FormatHelper.FindAllOccurrences method.

DataTableFormatProvider: One should be able to set the AllowDBNull property of each column.

Applying conditional formatting to different worksheets and exporting the file to XLSX results in a file with conditional formatting on the active sheet only. The conditional formatting on the rest of the worksheets is lost. 

The pie chart is not rendered correctly and is not converted to pdf as expected.

The format applied to the first value of the range of the chart determines the format of the value (vertical) axis. If the format of this value is changed, the model attempts to set a new format to the axis. If the chart does not support axes, the value of its PrimaryAxes property is null, which causes NullReferenceException.

Currently, indexed colors are imported only regarding the default color palette. Instead, when the entire palette is predefined using a construct like: 

  <colors>
    <indexedColors>
      <rgbColor rgb="00000000"/>
      ...

in styles.xml part, the indexed should be changed with the provided ones. As this feature is not implemented, such colors are changed during the import.

Chart not visible when file has OneCellAnchor xaml element.

Add API that allows one to manipulate the macros inside a Workbook.

SpreadProcessing: Upon export, sheet reference in formulas such as VLOOKUP is lost when using whole row/column references.
For example the formula
=VLOOKUP("test",Sheet1!A:C,1,0) is exported as

=VLOOKUP("test",A:C,1,0)

When a file is imported that has an unsupported theme color type, the resulting ThemableColor is null. This results in a NullReferenceException on export.

If a cell has a style set (e.g. Bad) and no fill set on the same cell, after import and export, the no fill setting will be lost and the cell will be shown with its cell style instead.

With the current implementation, the Notes support only a rectangular shape.

Examples:

For cell values like 0001 stored as text, excel will show the error checking options as a green ribbon in the top left corner of the cell. If we click on Ignore Error, the green color ribbon on Top-Left side of the cell will go away. Add support for this to be preserved in the document.

Wrong UsedCellRange when the worksheet contains a DataValidation rule.

SpreadProcessing: Copying a cell with a LessThan conditional formatting rule throws a Null reference exception

Changing the sheet name with a string that needs to be escaped results in an invalid file due to missing escaping in the RefersTo value.

When a file makes use of differential formats an Index out of range error may be thrown on import.

Currently, the only way to set a culture for the SpreadProcessing is through the static property FormatHelper.CultureHelper. That way the value is shared between all instances of the SpreadProcessing. There has to be an API allowing to set different cultures for the different instances of the SpreadProcessing.