Resolution issue...

I have a mid 2010 27" Core i7 and have noticed an issue with resolution. My resolution for my login is 2560x1440, but my wife's is lower. Whenever I logout of hers and log into mine, my resolution is whatever hers is set at and have to do a restart to get back to full res. I noticed it in SL, but also does it in Lion. I also notice my wallpaper is small in the upper right corner of the screen when logging back in to my login and has only happened since upgrading to Lion. Any help would be appreciated. Thanks