so I must supoose that Your mouse cursor is to far away from the sketch lines.
Quick Pic only can show what is nearby the mouse cursor peak.
Come closer to th eskecth and You will see it.
No matter how hard I tried, it didn't work. I attached a video file about it.
But in the meantime I upgraded to ST10 academic, opened the assembly I made earlier with ST8, did the same exact thing and voila this time it worked.
Anyway I accept your answer as a solution, because of your video.
Thank you all for your help, you are a really great community.