At last...I've managed to fix this theme of all it's bugs and odd behaviour, mainly caused by my misunderstanding of the way the various page-layouts are calculated. As this theme uses percentages rather than pixels, and considering I have a degree in mathematics, I should have known better. It makes sense to read the formula rather than assume too much!
Having got thus far with this theme, I personally feel I have made a breakthrough, in that I can confidently go on to design better themes from now on, given the new tools that Sam has produced, is still producing, not to mention his tutorials too!
Thanks to everyone for their help and support.