I have noticed this before as well. When a question is marked duplicate and closed, the possible duplicate question appears at the beginning of the post but there is a math typesetting error when it inserts the duplicate link at the beginning of the post. (Theo Buehler and Artuto did the edit for it to appear properly but I undid it so that the bug can be seen)
The same problem occurs for this question as well http://math.stackexchange.com/questions/37630/how-to-express-log-p-q-if-log-p-4-m-and-log-sqrt2-q-n
Another evidence of this bug
I reported this on the meta of math.stackexchange as well but no action was taken.