Draw Inside + Blob Brush bug

Hello,
I believe that the Blob brush "merging feature" with the same fill color is a bit too aggressive, so much that I'm considering it a bug. 
In the attached example, I have the neck selected and I intentionally set it to "Draw Inside" because I only intend to paint inside of it. the problem is that "Draw behind" gets circumvented when I paint with the same color (the darker color here) that an area outside the "Draw behind" area has (the face shadow). 

In such a scenario, the expected behavior is that we remain within the masked area, and the blob brush would only join with paths with similar fill that are within that mask.

Should I post this bug in https://illustrator.uservoice.com/ or would it be seen here?