Hi Trender,
The first thing I would note is that you are back-testing a large period – around 10 years – in one go. There are limitations on how much data MT4 can process and it is most likely you are running into some issues here. You can see here for further information on this: http://www.tickstory.com/forum/viewtopic.php?f=4&t=462.
To answer your question, there should be no difference in the Open and Close prices of the 1-minute bars. The bars are constructed from the time-stamps of each tick that occur within each minute. Once you resolved the issue above, if you are still having discrepancies I would suggest you analyse a few trades and compare the timing of the trades. Bear in mind that if your EA is somehow dependent on the starting date (for eg. it only takes a trade if the last trade was successful), then will you obviously get different results depending on the range you select.
Hope this helps.
