how do u tell what geometry will stay when escaping and what will vanish?

[Seedy steve]

I've noticed that some things like a line will not disappear when u escape out of the line manager but other stuff like letters will vanish unless u click that stupid green check mark.

( I call it stupid because it randomly works with enter and mostly not.) I wonder how to tell when that will work too. And why can't it  always work?

[Seedy steve]

How much other stuff is unpredictable or random in MC ? 

like the way the arrow of doom jumps around sometimes and not others. If I want to move it I would rather do it myself!