This has been frustrating me for a while (I think it was introduced in 2015.5), but there still isn't a fix: When you are painting with the brush tool and you use the icon in the toolbar to toggle pen pressure, that value is no longer synced with the Shape Dynamics toggle in the Brush panel. it used to be, and the Opacity toggle still is, it's just the Pressure toggle that's broken. It'll turn on but it won't ever turn off unless I open up the Brush panel and do it there, very cumbersome and annoying.
Below is a video of the problem. Happens either when you click the toggle buttons or use the newly-added keyboard shortcut option.