If you've upgraded to the Lightroom's latest version of Lightroom 4 and you're experiencing problems with using a Wacom pen tablet with it, then this very simple fix might help you - at least it helped me. For some odd reason, my pre-defined key's and shortcuts on my Wacom pen tablet didn't work at all or did different things when I upgraded to Lightroom 4. I spent hours googling, searching forums, etc. until I came up myself with this easy fix that worked for me. Wait for it.... just go to Wacom's website and head to the Driver section to download the latest installation and driver files for your Wacom product (for Europe-based customers, you can go here). Just re-install and upgrade the drivers and software, restart your computer (unusual for Macs, I even had to restart my Macbook Pro) and enjoy your Wacom pen tablet as it was before you upgraded to Lightroom 4. Yes, it is so simple :)

I'm not sure why my Wacom pen tablet didn't behave in the same way with Lightroom 4 as it did with Lightroom 3. I think it could have been an outdated Wacom's driver or software.