I found an example of something broken by the addition of "height: 100%;": the jQuery test suite embedded in the playground server no longer has a vertical scroll bar, since the height is fixed and the overflow is hidden.
I really think that Caja adding such properties by default is the wrong thing; the host page should be responsible for setting them (or asking Caja to do so since it knows about the double-div) so that things operate according to the unaltered HTML/CSS model by default. As I mentioned before, the host page, if it does anything nontrivial in its own markup, will have to take particular care to ensure a gadget can be 100% height anyway.
