That's a gnarly bug! Thanks for the report. I'll try it on 2018.2.5 to see if I can reproduce it. In the meantime you can try Unity 2017.1 and see if it works OK there.
Thank you for the quick reply! I'll try with another version and report how it was going.
Anyway, thank you for such cool app
UPD: for Unity version 2017.1.5f1
Just checked with another version. There is the same issue too, but slightly different which is weird.
If I click on the particular frame with my touchpad(not tablet), frames won't change unit I draw one line and after that -- same behavior.
However, with this, I at least can calmly draw one line, heh.
I upload another video with it: google drive