Within the Customized World type's, "Customize", option, when attempting to set a biome for the world and exiting the screen after finishing, the setting remembers another option. For example, I set it to Ice Plains and was rewarded with a world of the Mushroom Island. After checking the cause, I have noticed that a few biome settings do not remember correctly.

-Set World type to, "Customized", and select Customize.
-Change Biome to, "Ice Plains" (or one bearing the odd quality).
-Click, "Done", and either generate the world or re-enter the Customize options.

*I have discovered no crashing and biome selections down the list appear to work efficiently (excluding the oddities akin to the stated scenario).