Is It Monday, Last Friday Or 1974?

A real quick way to mess with your own mind is to watch a movie about changing past events/memories for the second time and have it come out with a different ending than you recall.
This weekend, I paid a visit to the only video store in town that will still let me hire from them. The guy who owns this store does not enjoy my patronage and, well, rightly so. I have a wee problem with the returning part of the whole rental transaction which has left me blackballed at Blockbuster, Video Ezy and Civic Video stores Australia-wide. This guy, however, is in a precarious position, being an independent with a so-so selection situated 4 doors down the road from a Blockbuster, and as such, he’s forced to tolerate what no one else will. Neither of us is winning on this deal. I’m hiring a number of pricey new releases that rarely make it from the plastic bag they were brought home in to my DVD player and he’s too worried about losing customers to charge the full late fees that I should incur. We’re both paying for a whole lot of nothing but it’s a little game I can’t seem to stop playing.
That said, I restrained myself this weekend and hired only one DVD. It was The Butterfly Effect. I had seen this movie when it was in the theatres but looking at the DVD case in the store I couldn’t recall a single scene. Later at home, when the first scene started, it all came back to me. The basic gist is that the main character finds a way to return to certain scenes in his life and alter his actions therefore changing the present, hence the butterfly effect. However, the ending I watched this weekend is completely different from the ending I thought I saw in the theatre. So I'm asking myself: Was this a different version released for US audiences? Was this the production company’s way of messing with the audiences head? Or did I imagine the original ending? Probably the former but, I tell you, after watching all that memory manipulation and parallel conclusions; its still got me feeling a little uneasy.