Chat window divider forced to be a set size

In the chat window, you can resize the area in which you are able to type, but as soon as you click again int he typing area, it jumps back to a set size.

Looking at the Spark code, I see that the dividerLocation variable in LayoutSettings.java is forced to -1. I assume that this might have something to do with it. Does anyone know why this is set this way or how it could be modified?

Thanks - ATM