I have had similar problems, particularly cross browser, with SSRS. The standard of the HTML generated is very poor and hence often is quirky to say the least even in internet explorer.
The client I was working for had strict standards for accessibility and browser compatibility so I looked into improving the standard of what was outputted a lot but didn't get anywhere. As reports are basically XML I was hoping someone somewhere may have written a better engine to transform this into XHTML but it appears not.
I ended up playing around with table size and column widths which in some cases seemed to resolve some of my issues.