My wife has an iphone also connected to Office 365 Exchange Online. I have her calendar integrated on my Z10 as well. Events that she creates on her iphone show on my Z10 in GMT. Events that I create on my Z10 show on her calendar in GMT.
It seems that when the event is created and sent to the server, the server converts the time to a "GMT Equivalent", but when it comes back to the phone, the phone doesn't convert it back to local time, if that makes sense.
The fact that both BB10 and iOS calendars are programmed to warn us of this via a disclaimer on the event details, tells me that it is some kind of limitation of Exchange technology that isn't going to get fixed anytime soon. My old BlackBerry 9900 did not warn me the same way as what is seen in the screenshot below. My wife's iPhone displays a similar message too.
Posted via CB10