Excel exports shapes as TwoCellAnchor elements, which specifies the top left and the bottom right location of a shape. The size of the shape is recorded in the extents element (a:ext), cx and cy attributes. At the moment, the spreadsheet import first looks at the extents element and if it doesn't find the size there, calculates it from the TwoCellAnchor element. 

However, if an XLSX document has a shape with incorrect size indicated in the extents element, Excel will still be able to open it correctly, probably because it looks at the TwoCellAnchor element. RadSpreadsheet/SpreadProcessing, on the other hand, will show the image with an incorrect size.