It's not clear to me from your node if you mean that the formulas are not preserved, or the values computed from the formulas are not preserved (in other words, the results are not preserved). If you are using Spreadsheet::WriteExcel to write out the Excel binary format, then you should it's important to know that this module does not store results with the formula. The documentation for Spreadsheet::ParseExcel mentions this and notes that the behavior is the same as if you had "Auto Calculation" off.

Update: Changed some language to avoid possible misinterpretation of tone.