Using Quicken Classic Deluxe (Canadian) on Windows 11. This has been going on for as long as I can remember.
I download the .qfx from Interactive Brokers for my USD denominated account. I accept the transactions and after verifying the details, I change the transaction from cleared to reconciled and then "enter". When I come back to this transaction, what was the correct exchange rate has been changed to 1.0000. As a workaround, I believe that if I remember to click inside the exchange rate field before marking it reconciled the correct exchange rate is saved.
As a side note, I often get a pop-up verifying if I want to change a reconciled transaction. I usually find that the functionality is strange. I usually have to click "no" to get my changes entered.