Why do some calendar events shift in time when daylight saving time goes into effect?

Recently the UK changed from winter time to summer time, I have noticed that the timing of **some** of my calendar appointments (Google Calendar via Google Sync) have also been shifted forwards by an hour, whereas some have not changed. It could well be that the split is down to events created on the iPhone and those created on the Google Calendar web interface. Does anyone know a work around for this, that will stop me turning up an hour early to things when the clocks change back in October?