When things act strange and also to help prevent things from acting strange I always repair my permissions. I have head various "dosage" recommendations for doing this, but I will do it at least once a day, and more than often 2 or 3 times, especially when I am dealing with big projects or plugging and unplugging external drives. It is a good habit to get into for healthy machine living.

First, select your Disk Utility icon from your Dock. If the Disk Utility icon is not there, it should be. You can get it from your Applications > Utilities folder.

This window will pop up, select your Macintosh HD

Then click on Repair Disk Permissions. It takes a little time for the permissions to be repaired if you haven't don it in awhile. After it is finished I may or may not restart depending on the funkiness of the problem or the time I have.