editing info in photos (Mac)

I have a problem which has driven me nuts for months. and its a problem I have had on different Macs so I can only assume its a software issue. Every time I try and edit the info on a photo, I can't complete it because after typing a few letters it stops allowing me to continue. it keeps "booting me out of the field". Its really hard to explain. I try and start typing and then it just stops working and sometimes tries to do other actions like asking me if I want to delete the photo. I can't edit titles, cannot assign a location. it just won't let me complete more than a few letters. Driving me insane! anyone have an ideas?