I have same issue on test machine and I'm using EST.
to_date is a string function that's taking your date and converts it to a date, though it still has its time values (setting its hours to 00:00:00). However, when WIndchill wants to display it, it uses that date as a GMT date and gives out the GMT date converted to your time. As you notice, its still giving you the hours and timezone in the result.
You therefore need to strip the time data from the object when you want to display it. I tried 2 approaches
1. convert using To_Date function, then get substring of first 10 characters.
2. just get substring of first 10 characters from date.
As you can see, this results in 2 different outpus, though the second on formats it according to your standards. I also tried out concatenating it with another string, and that works also, though you don't need the To_Date function.