Typing 2e-1 returns 4,43656365691809047072. It treats "e" as the constant.
Typing 2e+1 returns 20.
So, when typing "e" the popup shows the constant unless it is followed by the plus sign which then becomes the scientific notation e.
SpeedCrunch master (Qt 5.8.0)
MacOS 10.12.5 (16F73)