How did the times of my photos get changed?

Got back from Europe, uploaded my iPhone camera to iPhoto on my iMac. In Events I am finding that a number of photos, and series of photos are out of order--the times they were taken are not consistent with others in their series. How does this happen? I had the iPhone clock set to local time in Europe. Does weirdness happen when you get back to the States and change the time back if you do it before off-loading photos?

I did figure out how to change the date/time, but in order for it to have an effect on the display order you have to leave the page and come back.