As I think you are already aware - there was an issue with the autogrow setting being converted to a very large number. If you have already patched beyond that point, then the only other reason that the autogrow setting could change is if some process is changing it.

Also, be aware that a database will only grow when it has run out of space and it needs more space. If your database is growing, then you must have a process running that needs additional space available - causing the autogrow event to occur.

What I do is make sure the autogrow setting is a much higher value than 100mb. With instant initialization available and a 380GB database, I would set my autogrow to at least 5000MB - then I would manually grow the file to maintain at least 20% (or 6 months, whichever is larger) of data space available in the data file. I then monitor the database on a regular basis and schedule time to manually grow the file as needed.