Simple Round Pen Behaves Different For White and Black

Hi,
When using colored background, the Simple Round Pen behaves differently for black and for white. Black performs as expected, but white has a "halo" on it.

Is this a known bug or is there a setting I don't know about?
Thanks!
When using colored background, the Simple Round Pen behaves differently for black and for white. Black performs as expected, but white has a "halo" on it.

Is this a known bug or is there a setting I don't know about?
Thanks!