Steps to Reproduce:
1) Create a blank Site
2) In this Site, create a new category in the "Topic" vocabulary
3) Create a new Web Content with the word "test" as the title/content and add the category created before
4) Copy this Web Content twice, now there's 3 Web Contents that has the same category
5) Create a new Page and add the Search Portlet
6) Search in this Site for the word "test"
In the Categories result, there's only one Web Content, but should have three.
Note: Couldn't reproduce in 6.2 EE SP1, it shows three Web Contents in the Categories results as expected.