I am getting crazy with this problem. Recently I bought a Intous Pro Medium, and using it Photoshop CS6 (64-bit) When using the brush tool (standard round brush, size and opacity jitter set to "pen pressure"), I have found that every so often my marks will come out heavy and opaque regardless of how hard I press down with the pen. It doesn't occur on every stroke, and if I make a mark immediately afterwards the pressure sensitivity appears to be working just fine again. For example if I am doing a black and white line sketch, some of my lines will come out solid black when I intend them to be light and gray. I was looking in internet for a solution to this issue but there was just some tips that experiments from 2012. Some promises of Wacom that will fix it in the next driver (also 2012) and from Adobe just excuses.
Somebody knows a real solution to this problem? I use PS CS in Windows 8.1