The CSS evaluation algorithm of HtmlUnit doesn't care about the current CSS setting.
In my understanding, if I disable CSS for my webclient instance then no CSS evaluation should be happen at all.
I have attached a testcase to demonstrate this issue. Please note, that only CSS declarations embedded using the "style" attribute will be evaluated by a CSS disabled webclient.
JUnit test case
HTML resource used by JUnit test case
Fixed in SVN, thanks for the very simple test case.