I have last version of Adobe Lightroom CC.
Steps to reproduce bug:
1. Enable profile corrections.
2. Make some changes in Distortion.
3. Make some changes in Crop mode - correct angle.
4. Select Brush and start selecting at the edge of photo.
Area marked as square during selection.
I am not seeing anything wrong happen when I try what I interpret your steps to be, but I may be misinterpreting something.
1. Enable Profile corrections - this is easy enough to understand.
2. Make some changes in Distortion. Which Distortion, the one on the Profile tab or the one on the Manual tab? The lens I'm testing the raw from has very little distortion to correct so if the Profile - Distortion slider is what you mean then I may not see anything wrong because so little was changed when I moved the Profile - Distortion slider. I can make significant changes using the Manual - Distortion slider but again I don't see anything wrong with the brush stroke, later.
3. Make some changes in Crop mode - correct angle. Are you saying the change the Angle slider in the Crop area? I set mine to 45-degrees and am not seeing anything wrong at the edges of the Crop area regarding an adjustment brush stroke?
Here is what I end up with, where I've changed things back to "Crop mode" so as to show what the brush stroke looks like beyond the edges of the cropbox: