Solver limitation on dependent constraints?

[oCoCarbon]

I'm trying out the Evolutionary Solver in Excel 2010 and I'm running up against a problem. What I am trying to do is create a spreadsheet to optimise window sizes and ceiling heights for a room. As part of this, I need to constrain the window height to the ceiling height. This works just fine until I make the ceiling height variable.

Is this a limitation of the Solver engine? Can I not set a variable to be constrained by another variable.

The symptom is that Solver returns either no window at all, or a really huge one, and oddly it seems to alternate between these two. It is perfectly possible to find an answer by hand so it's not a problem with no solution as would normally be suggested by this kind of symptom.

Can anybody help?

 

[oCoCarbon]

To add some more info, I've tried contacting FrontLine and they don't seem to have an answer. They suggested making the problem simpler which I have done by removing all integer constraints and it still shows exactly the same behaviour.

Any Evolutionary Solver experts out there??