Hi - I installed Joomla 1.5.20, then installed only the YouBubble template. I then set 'Section Name' and 'Category Title' to "Show", and 'Section Title Linkable' and 'Category Title Linkable' to "Yes". As before, it all worked as expected.
Have you tried setting 'Search Engine Friendly URLs' to "No"? Beyond that, what extensions do you have installed, or what modifications have been made to any portion of the template?