An example from the Omni forum would be the current thread on the Masters golf tournament:

http://www.flyertalk.com/travel/fttr...ML/006322.html

About half way down the first page, Pinniped posted a link to a Yahoo news story - the URL was very long and thus caused the "widening" of the entire thread.

Sorry this isn't a more technical explanation, but I do think this is the reason some threads require us to scroll back and forth to read them.

This could be avoided if people used the "true hyperlink" method explained here:

http://www.flyertalk.com/travel/fttr...m/ubbcode.html