Some brushes have the top of their tip broken. It seems to happen only for brushes with pressure-to-size, when the brush is smaller than full size. (I could reproduce at least with Basic_circle, Fill_circle and Fill_block) See on this screenshot: http://timotheegiet.com/kritaB/bugBrushKrita.png Reproducible: Always
I can confirm.
Might be related to the Ratio Sensor functionality
I've asked Nishanth to look into it already.
Animtim said that it was fixed this morning. So closing this.