With LR 6 occasionally the adjustmend brush does unwanted strokes when mouse/wacom tablet pen is released. It occures irregularely and mainly in images which contain brush strokes already and new strokes need some seconds to get visible in the lack of brush speed.
Then it happens that I release the mouse (or lift up the wacom tablet pen) to move the cursor to a different location on the image and I get an unwanted stroke on this way. It is quite disturbing because this unwanted stroke again takes seconds to appear - then I often have started to use the brush at a different position already.
This did not occure in LR 4 to me.
MacBookPro 8,2 (2011), OSX 10.9.5, Wacom Intuos with last driver, LR catalogs & system on SSD.