Last modified: 2011-03-13 18:05:10 UTC
The merge() method of ParserOutput looks like it suffered from a copy-and-paste job in the implementation. The line that is supposed to merge category links from $other instead merges $this->mCategoryLinks with $this->mLanguageLinks. I will provide a one-line patch.
Created attachment 1242 [details] Patch for Parser.php to fix category links merge bug
ParserOutput::merge() is deprecated and has been removed from 1.6. Please find some other way to do whatever it is you're doing.