I am running Lightroom 4.1 on two Macs, both running 10.7.4. On one of the machines the Alt/Option key does not work properly in the Develop module.
When I hold down the Alt/Option key and move the Exposure or Blacks slider I expect to see the clipping display. Instead this action moves the whole of the sidebar of the user interface. I can move it to any place on the screen and off the edge of the screen. Clearly this should not be possible.
The problem machine has a Wacom Intuos 3 tablet attached, so I have tried updating the Wacom drivers, and also removing the Wacom software completely. Neither solves the problem. My other Mac does not exhibit this problem.
Try removing the Preference file so a new one is created, can cure unusual issues.
I've been hanging around this forum for a long time, and I've never seen anything like this.
Are you running any software "in background" that modifies how the user interface works?
Have you tried re-installing Lightroom? Normally, I wouldn't recommend it, but...
I tried reinstalling Lightroom, but that did not help.
I think I have narrowed down the cause to an interaction between the Wacom tablet software and a window management application called Flexiglass (which allows you to force windows to maximise fully and also gives some useful Windows 7 type window positioning options). If I either quit Flexiglass or unplug the tablet, the Alt/Option key works properly.