Give renewing your iPhoto preference file a shot -
A good general step for strange issues is to renew the iPhoto preference file - quit iPhoto and go to "your user name" ==> library ==> preferences ==> com.apple.iPhoto.plist and trash it - launch iPhoto which creates a fresh new default preference file and reset any personal preferences you have changed and if you have moved the iPhoto library repoint to it. This may help
This does not affect your photos or any database information (keywords, faces, places, ratings, etc) in any way - they are stored in the iPhoto library - the iPhoto preference file simply controls how iPhoto works - which is why renewing it is a good first step.
LN