The article below outlines a useful technique in identifying and resolving CSS ‘bugs’ and other problems.
From the article overview:
Mystery Bug – css-discuss
CSS bugs can be obscenely difficult to isolate, especially when they are located amidst a large, complex page with many external style sheets. Compounding this is the fact that few coders have enough experience to be sure that what they’re seeing really IS a bug, and not just incorrect coding.Often people will, when facing the Mystery Bug, just thrash about almost blindly, and only by pure luck will the answer be found. This need not be.
By following the procedure below, a clear understanding of the problem may be quickly obtained, freeing the coder to find a workaround or avoid the bug altogether.