Steps:

1) Start minecraft in demo mode :

java -cp .minecraft/bin/minecraft.jar:.minecraft/bin/lwjgl.jar:.minecraft/bin/lwjgl_util.jar:.minecraft/bin/jinput.jar: -Djava.library.path=.minecraft/bin/natives net.minecraft.client.Minecraft - - -demo

2) Resize the window to have something like a 4:3 window
3) start a new world and look at the text and buttons

The window position calculation and text position calculation seems to be diferent, so they are placed in different places.

Having the text in the window like in 16:9

The text is out of the window