Gah Every update it seems SOE want to make PS2 worse for me. With the latest hotfix the return key now seems to be hard mapped to window mode. A key I have set up for jump. I just don't understand it, has anyone else found out where it is in the options to turn off? and just why they have done this in the first place?
Run your Planetside 2 Launchpad and log in, but do not press play. Click on the Advanced Tools icon (looks like a hexagon surrounding a wrench) in the lower left and then choose the option to open game directory. In the window/folder that comes up, you may want to make backups of, locate, and delete the following files PlanetSide2.exe ActivityUserData.ini LaunchPad-user.ini LoadingScreen.xml InputProfiles.xml SoundSettings.xml UserOptions.ini vivoxoal.dll vivoxsdk.dll Once these files are deleted, close the Planetside 2 window/folder and go back to the Launchpad > Advanced Tools/Settings menu. Click on the Validate Game Assets menu option and then press the green Validate button to have the Launchpad check your game files, and download any missing or corrupt files.
As far as I can tell, there has been no change to this. The return key is not hard-bound to anything. Alt + Enter, however, is the default shortcut within Windows to switch between windowed and full screen modes. You might want to make sure there isn't a problem with one of your keyboard's Alt keys. As Jesse has suggested though, this may also be an issue with settings files. If neither of these suggestions seems to resolve it, please submit a ticket using the link in my signature so we can look into this.