A: 

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.

AJM
Sorry for not accepting the answer sooner... I haven't had time to visit the specific client's site since asking the question so I haven't been able to try you suggest solution. But I reckon it's a possible way to go forward and I can always retract the acceptance if it turns out to be fail.
Dan Sydner
A: 

Upon further inspection it seems that all numbers are enclosed in divs, with the attribute width=100%. Using the developer tool in IE I saw that removing width=100% restored the borders.

One solution could be to write your own renderer based on the standard html and filter out the annoying little buggers.

Dan Sydner
sorry for answering my own question...
Dan Sydner