Why Does Excel Recalculate When Opening a CSV File?

I am running Excel 2007, working on an .XLSM file that was originally created as an .XLSX file in a later version (it includes some formulas using UNIQUE and FILTER functions, which are not recognized by my version of Excel).
It takes a significant time to recalculate (about 10 seconds), and it recalculates every time you change ANYTHING (so I'm guessing it has some other volatile functions somewhere).
I have it set to manual recalculation so I can work on it efficiently.
If I open another .XLSX file (while this main file is open), that file opens immediately (although it does show "Calculate" due to the manual calculation).
BUT if I open a CSV file (manually, or through a macro), Excel recalculates the main file each time (before opening the CSV file). Even when the main file is set to manual recalculation!
Since I've set up a macro that loads data from 7 different CSV files (into this main file), this recalculation delay means that the macro, which should run in about 1 second, takes well over a minute to complete.

Can anyone shed light on (1) WHY does Excel recalculate (in manual calculation mode) when opening a CSV file, and (2) is there anything I can add to the macro code to avoid this?

Thanks for the tip about importing the data (rather than opening the CSV file directly)! I do need to check the data and pull it into specific columns, but if all else fails, I can always import the raw CSV data to a blank worksheet, and then check / manipulate it from there (like I would do from the opened CSV file).