I presume you're on a Mac, this is a bug with newer versions of forge. You have two options; either press F3+t when you first load up your world, or go into the configs folder for the pack and edit the splash.properties file and change the line
I'm not on a mac to test it myself, nor have I heard feedback from anyone who's used that fix to no, but AFAIK it probably requires being done each time you boot up the game.