If the inner rect of a window changes due to a reason other than regular sizing event, the change is not communicated in any way, and content is not updated.
Easiest way to reproduce this is to set up a "inner_rect" NamedArea with some dimension or other tied to a PropertyDefiniton. Manipulating the property changes the area, but regular window content (defined in layout or code) does not have its position and size updated accordingly.
I believe that the issue here does not lie in the use of the property, but rather that the changing area should be detected and handled somehow.
Additional information: See: http://www.cegui.org.uk/phpBB2/viewtopic.php?f=2&t=6126
Also: This is not an issue with the PropertyDefintion layoutOnWrite functionality. That is defined as affecting children defined in the WidgetLook, not regular child content, so in this regard, the functionality of that feature is working as intended.