Ah, I think I may have found the problem - I had a repeat region at the end of the select list (don't ask me why, it's a couple of weeks since I built this!) which I've removed and now the dropdown is showing the text value - but I now have another problem in that it's not necessarily showing the correct city/country info because some of the timezones share the same value. Simple fix I think is to group together those that have the same values (I used a standard timezone list from another site to build this).