Spreadsheet gear Chart's x axis date is appearing as whole number

Spreadsheet gear Chart's x axis date is appearing as whole number

I am generating an output using spreadsheet gear which contains chart as
output and its XAxis has date and y axis has numbers to plot the chart. At
the end, application will copies the source workbook sheets to new
workbook's spreadsheet. While doing this, the date values in the chart's
XAxis is not appearing as date (MM/dd/yy) in the sheet which i have copied
(i.e. in new workbook's sheet), instead, i am getting it as some number
(such as 39174, 39175, 39176. Could this be a julian date?). Even though i
am formatting the Date column to a Date format (MM/dd/yy), but still it is
not referred as date in the graph. I have cross checked this by right
clicking on a cell (in Date column) and choosing 'format cells' option. It
is showing that it has used custom formatting (as mm/dd/yy) for it. Also,
i have coded to update the links while copying it to a new sheet, but
still it is not working.
Please advise to resolve this issue.
Thanks