Custom workout estimated distance messed up if the target is not pace (or speed)

Hello everyone,

I am trying to create workouts via the Garmin Connect Web App. 
I am building steps with different targets, and I am always getting some very very messed up estimated distance calculations, if the steps I am building are not based on pace or speed.

Below are some examples. 

Running workouts:

It would be very useful to have the estimated distance, in order to decide the course that I can do for the workout... This seems to be basic stuff: No one is running 120km in 10minutes, and Garmin has all the data from my runs. 

Garmin please fix this, or please help me fix this...


Appreciate your attention and thanks in advance.