Two things, reported to me by bbundle players concerning v4 but are probably present in v5 as they are to do with the world creation GUI:
(quote below from bbundle MCF thread)
BUG #1 You can not create a vanilla CUSTOM flat world
The menu loops back to world generator selection instead of "Create New World" when you try to create a custom flat world.
BUG #2 - Options such as difficulty, survival, etc. missing during world creation
VERSION of TC Affected BUG's # 1 & 2:
terraincontrol-common-2.7.2 for Forge 1.7.10 v4.jar
terraincontrol-forge-2.7.2 for Forge 1.7.10 v4.jar
Click "Singleplayer" at the main menu.
Click "Create New World"
Click "More World Options..."
Click "World Type: Defult" It will then change the button text to "World Type: Superflat"
Click "Customize" Click "Presets" Click "Overworld"
Click "Use Preset" Click "Done"
You arrive back at the World Generator Selection returning you to step 3 above. This loops you and you have to enter all your selections again /loop infinity