My Exchange host has been working on this with top-tier Engineering support at Apple for 2 weeks now. It appears that the particular tech he is working with agrees this is a bug in iOS 8.
Unfortunately, the techs aren't sharing information with each other. My Exchange host informed me that another one of his clients...working this identical bug through a separate support case was told the following by Apple:
"The customer is contacting us because both the local time, and either the time of the originator or the server
is showing in the Calendar app. This is expected behavior with iOS 8."The customer can submit feedback on this feature at http://www.apple.com/feedback."
The above confirms a few things:
1. The tech writing this response clearly does not understand the issue being reported
2. The tech expects the customer to believe that the time transposition to something OTHER than selected by a user is a "feature"
3. The tech has no interest in acknowledging the problem and/or doing anything to further iinvestigate or fix it
My suggestion: USE THAT FEEDBACK LINK and report this! The more people Apple hears from, the more likely they are to do anything about this. As of now, they have made it clear that they don't care.
Also, I have posted a video on YouTube demonstrating this bug, and confirming this is ONLY generated by iOS devices. If you want to check it out, here's the link: http://youtu.be/cgP1zyi_iV8
Finally, most tech websites have TIP links. Go to the tip links and REPORT THIS BUG and Apple's attitude toward fixing it. If even one site publishes a story about this you can bet Apple will finally address it.
And Apple, consider this: the way I originally found this discussion thread...and the way many others find it ... is by Google searching "iOS 8 Calendar bug GMT." As of right this second the thread has been viewed 18,498 times according to the stats at the top of this page. Think this is an isolated issue? This is affecting thousands of your loyal customers. We'd appreciate it if you would respond with something more encouraging than "Thanks for being an Apple customer, go pound sand."