FM12 has some performance problems that appear to be related to how much calculation is required to display data.
I created two simple test files that contain a conditional format calc that increments a global variable.
The global variable is displayed as a merge field on the layouts.
The difference in behavior between FM11 an FM12 is interesting and startling.
Try the files: try resizing windows, navigating between records, using layouts where the formatter calc is in line or only in the header.
In some cases in FM12 a single refresh may cause the variable to increment by 10.
There is a script in each file to reset the variable.