Creating animation by dropping sprites on Scene view generates broken timeline

Hello there!

I'm working on a mini game with my students on version 2019.3.18f1 and we have an issue while creating the fist animation of my character by drag and dropping the 3 frames of a walk cycle directly on the scene. I'm prompted to save the animation as usual but after that I have a broken timeline. As you can see on the screen shot time jumps directly from 0:10 to 1:00

7502489--924416--upload_2021-9-17_13-56-17.png

If I create another animation for this character from the dropdown menu of the animation window > Create new Clip all is OK. Timeline is correct on the new created Clip.

7502489--924419--upload_2021-9-17_13-57-50.png

My first guess is that it is a bug, but maybe I'm missing something ?
I can reproduce this 100% on my end.

Have a great day!

Anyone ?