C#: TimeZoneInfo.GetSystemTimeZones()

TimeZoneInfo.GetSystemTimeZones() returns a reference to a same instance, no matter how many times it is called.

When the time zone list is added to combo boxes, they select the same values.

comboBox1.DataSource = TimeZoneInfo.GetSystemTimeZones();
comboBox2.DataSource = TimeZoneInfo.GetSystemTimeZones();

The Collection class must be copied to some other forms.

System.Collections.ObjectModel.ReadOnlyCollection list 
= TimeZoneInfo.GetSystemTimeZones();
TimeZoneInfo[] tzList = list.ToArray();
comboBox1.Items.AddRange(tzList);
comboBox2.Items.AddRange(tzList);