Excel app opens when opening file from IDE

Strange thing happening when running IDE in VCL mode on Windows 10 machine.
When using an Excel file with Flexcel at runtime, an instance of the Excel application will sometimes open separately. I've not seen this or had it reported to us when using the compiled app - only when running within the IDE.
Is this something you've seen? It does not happen when using any other format of file.

Unless you have FlexCel 2 (I hope not...) it is not really possible for FlexCel to open Excel in the IDE. FlexCel doesn't know anything about Excel (that's why it can run without Excel being installed or in platforms like iOS or Android). FlexCel just opens the files as an array of bytes, parses the file, manipulates it, and saves it back. It never calls any Excel Automation API or any special Windows API, it just manipulates bytes. It can't open Excel.

Now, if you are seeing instances of Excel opening, this is likely some OLE automation call indeed. As said, it is not FlexCel, but it probably is something else calling OLE. It might be some OLE Automation code you have (maybe some old code), or some component that under the hood is calling OLE Automation. Say, for example AdvString.SaveToXLS (or similar, I don't remember the exact name of the method) uses OLE Automation to save as xls.

Finally, if it is only happening with the IDE, it might be a design-time component that is connecting to Excel while at design?