What is your default calendar?
I think your are describing the same annoying problem that I noticed after my most recent upgrades. When my Yosemite or IOS 8 device generated a calendar entry, the entry was in the correct time slot but the time was listed in GMT. I realized this happened when gmail used Apple Calendar to create an entry in my gmail (default) calendar. The problem seems to have disappeared when I switched the default calendar to iCloud-based. I'm not happy about this, but so far it's worked. It would appear Apple is "crowding" users into Apple based programs.