Don't report data table master cells as formula cells, since POI doesn't evaluate data table formulas.

ooxml/XSSF/UserModel/XSSFCell.cs

@@ -759,12 +759,22 @@ namespace NPOI.XSSF.UserModel
                 }
             }
         }
-
+        /// <summary>
+        /// POI currently supports these formula types:
+        /// <list type="bullet">
+        /// <item><description> <see cref="ST_CellFormulaType.normal" /></description></item>
+        /// <item><description> <see cref="ST_CellFormulaType.shared" /></description></item>
+        /// <item><description> <see cref="ST_CellFormulaType.array" /></description></item>
+        /// </list>
+        /// POI does not support <see cref="ST_CellFormulaType.dataTable" /> formulas.
+        /// </summary>
+        /// <return>true if the cell is of a formula type POI can handle
+        /// </return>
         private bool IsFormulaCell
         {
             get
             {
-                if (_cell.f != null || ((XSSFSheet)Sheet).IsCellInArrayFormulaContext(this))
+                if ((_cell.f != null && _cell.f.t != ST_CellFormulaType.dataTable) || ((XSSFSheet)Sheet).IsCellInArrayFormulaContext(this))
                 {
                     return true;
                 }
@@ -773,7 +783,12 @@ namespace NPOI.XSSF.UserModel
             
         }
         /// <summary>
-        /// Return the cell type.
+        /// Return the cell type.  Tables in an array formula return
+        /// <see cref="CellType.FORMULA" /> for all cells, even though the formula is only defined
+        /// in the OOXML file for the top left cell of the array.
+        /// <para>
+        /// NOTE: POI does not support data table formulas.
+        /// Cells in a data table appear to POI as plain cells typed from their cached value.</para>
         /// </summary>
         public CellType CellType
         {