Help -ALT tags misbehave-

Hello

I am still trying to tidy up my HTML on a web site. I have 'alt' tags
wherever required. I have an included *.shtml footer which is an image
map. The alt tags for the links in te . However, they only appear if
the page is short (even though the HTML is the same).

Check it out 
A short page: http://www.trentu.ca/csd/webct/instruct/
A long page : http://www.trentu.ca/csd/webct/instruct/whatmy.shtml

Thanks,
Amine Laghaout