Your browser does not seem to support JavaScript. As a result, your viewing experience will be diminished, and you have been placed in read-only mode.
Please download a browser that supports JavaScript, or enable it if it's disabled (i.e. NoScript).
Ahh yeah that's a bit confusing, the merge topic tool can be used between categories, so you should click merge first and then select the topics. The placement seems like a theme/skin issue.