After selecting a timezone explicitly unable to revert back to default timezone under user profile

Summary

After changing a user's timezone from default to a specific timezone (eg. america/chicago) in the UI, user is unable to change the timezone back to default (etc/utc)

Steps to reproduce

1. In FishEye/Crucible go to Profile settings > Display Settings
2. Select a timezone other than default and click "close"
3. Go back to display settings and select default (etc/utc) timezone and click "close"

Expected Results

Timezone setting is reverted back to default

Actual Results

Other timezone (eg. america/chicago) remains set