Where is IST (GMT + 05.5)

I was filling a form in a website and found the drop down list for timezone has listed all timezones which differs from GMT by a multiple of an hour. So many timezones which differs by a multiple of an hour plus 30 minutes are out of the list, and IST (GMT + 05.5) is out of the list. So how can I feel it? One thing I am thinking, the developer who developed that form is unaware of all timezones, or thinks every timezone only differs by a multiple of an hour? Or it may be an error while coding which makes those timezones out?