here's a couple of things to try
install the plugin on this page Menus, shortcuts, Lasso tool, or Photoshop stop working when using a Wacom tablet | Mac OS
downgrade your Wacom driver to
Wacom is not the problem. It’s the keyboard short cuts that come with cs6. They worked fine until I upgraded my os to Yosemite. My tablet works fine as before. I’m on a MacPro.
When I hit “x” the colors periodically don’t toggle black/white. V, B, Z, etc. do not work, periodically.
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Did you install the White Window Workaround plug-in?
Just did. So far so good. Thanks