I think perhaps Doug may be right, unfortunately. I have already tried re-assigning the keys so that is not the problem. It is only a speed problem but when I'm working quickly I like to use the tablet's function keys. For instance at the moment I am editing a school play with hundreds of pictures, and having to move my left hand backward and forward to the keyboard instead of just using my fingers on the express keys - it all adds up to increased time on a job. I feel sure I've never had so many problems when upgrading previous version of Lightroom. It is such a great piece of software that I'm willing to forgive it though, but next time will not upgrade for at least a few months.
Jim