Geocaching Australia

Trying to enter the character u with two dots above it into a post results in an error when posting (can preview okay, just can't post.)

An example of the character can be found in the name of this cache - http://geocaching.com.au/cache/gcw7q2 (try copying and pasting the name into a post.)

I wonder if phpBB3 has better UTF-8 support?

Correct and yes.
When we move to our new server we will be upgrading the forum software.
Until then, I'm afraid you'll have to accept the poor situation we are in.