(Space to see a similar error in white) (B to see it with a bitmap background) A random black pen line is drawn on a black background then the background is color cycled. See the line show up? Why is the background color cycling if it is pure black? For fun try setting the background to (0,0,0) aka pure black. Whee, now try setting the pen to (0,100,0) so it matches the black we are being forced to use for the vector (good luck). If you suspect this messes up color sensing you'd be correct.
I found a bug in how Scratch's editor is handling black in vector images https://scratch.mit.edu/discuss/topic/587350/?page=1#post-6112855 also found months ago by @colinmacc.. https://scratch.mit.edu/projects/633752135/
