The problem seems to be that you are using set_col() to set the format of cells that you have writing seperately.

Unfortunately, in the current implementation of the set_col() method doesn't work like this.

This is documented in the set_col() section of the documentation with the promise that it "will be fixed in a future release".

It will be fixed but in the meantime the best way to work around this is to store the column formats in a hash where the key is the column number. Then in your write_many() method use the appropriate column format if an explicit cell format isn't specified.

--
John.

Update: This behaviour was fixed in version 0.37 of Spreadsheet::WriteExcel.