Even if you correctly format a column, excel will ignore that if it sees something that looks like a date. That's part of the problem: this isn't just automatic formatting, it's very aggressive and hard to turn off. Plus you cannot revert the changes excel has made: turning 01/02 is converted to an ibt in 46000 range. So reformatting the cell doesn't get the original input back, it just lands you with a bunch of ints.

Back in the day I actually wrote a function that would undo this for some sheets that people kept breaking...