Same problem on all our iOS devices. This is strictly an iOS 8 error. We've ruled all else out.
Not due to Time Zone changes or "Time Zone Override"; none of the proposed fixes here work.
We're in the Pacific/"Cupertino" time zone. All Calendar events we create on our iPhones, iPads and computers (using iCal) show up correctly in our time zone on our computers (both in iCal and in Google Calendar on the web).
But events that use Google calendar accounts show up incorrectly on all of our iOS 8 devices: they switch to the GMT time zone. In some Calendar views, both time zones appear. This never happened before iOS 8 (or perhaps 8.1), and nothing else has changed.
NOTE:
1) We never leave the Pacific/"Cupertino" time zone, and have never set our time zones differently.
2) We've never used Time Zone Override.
3) When we create an event (whether using iCal or the iOS Calendar), our correct time zone is the only one displayed. But it switches to GMT in Calendar after the event is created.
4) Those same events still display correctly on iCal and in Google Calendar online. It's strictly an iOS 8 glitch.
5) We've tried every fix people have suggested here, including correcting an event's time zone, resetting iCloud, iOS and Google Calendar time zones, reinstalling, whispering sweet nothings into Siri's ear... nothing works.
This glitch renders the Calendar fairly useless. Needs a fix from Apple.
ETA: Yes, we've sent Apple Feedback on this. Everyone should:
http://www.apple.com/feedback/iphone.html
http://www.apple.com/feedback/ipad.html