What you have to be aware of is that everything in Final Cut has its own "viewport". Clips have a viewport and Titles/Generators have viewports. Anything that crosses outside of the viewport is cropped off. In fact, if you use an Effect to transform the position of a clip within its viewport, then try to apply **another effect** afterwards to restore the position, any content that went outside the viewport is never seen again! (until you remove the effects and use a different method).
For a Title, the viewport is your project's size. If you alter it's position (including Z position), scale, or crop settings in the Effects inspector, you are changing where in space or the size that viewport is, and therefore also the boundaries at which content will disappear if moved/animated "out of frame". Example:

As I said, non-zero Crop settings will constrict that viewport even more.
You lose the "top" color on the 3D Text going to 2D because the Material > Front (and possibly Front Edge) no longer pertains to the font settings. Font Face settings are used instead. It really shouldn't matter if you're using 3D or 2D Text as it pertains to the concept of "viewport".