So I whipped up a little example of what I believe to be a bug. Ill have to test to make sure normal canvas context drawing does not do this (but to my knowledge currently it does not).
Basically we cant draw 1px width lines?
If you set the lineWidth to 1 it draws it at half opacity but 2 pixels in thickness, which is really odd.
If you set it to lineWidth 2 it draws the same thickness but at the correct collor.
If you set it to lineWidth 3 it does both but at 4 pixels high (which I think is closer, but it should be one pixel of the full alpha lineColor padded by 1px of half alpha lineColor
The control/expected example of a one pixel line is done with the fillRect below the other lines.
Go into the inspector and look at the dt under textures to see what I am talking about or take a look a this capture of it.
This just seems off because Im fairly sure that you can draw 1px thickness lines on a canvas context.