There is definitely a problem with Curvemeister 2 and CS4. Curvemeister 2 is more intimately tied to Photoshop's window layout, since it replaces Photoshop's image window with its own window. Curvemeister 3 does not have this problem, because its window llayout is independent of Photoshop's.
I don't have a workaround as yet, but there is a possibility that disabling tabs, and using the F key to rotate through the various window display options will fix the problem.
If I can do it in a reasonable amount of time, I will fix Curvemeister 2 to work with CS4, but I cannot promise this. When I have a free moment, I will see what is involved in fixing the problem. If I can't fix it, then it would be necessary to upgrade to Curvemeister 3 to use CS4.
Just to clarify- the current version of Curvemeister, version 3 works with CS4 - the problem being discussed is with older versions of Curvemeister, versions 2 and 1.