We frequently have questions that are crossposted, e.g. http://mathoverflow.net/questions/137414/systems-of-parameters-for-algebra-a#question.

The only options for now are to close as off-topic, leaving a comment pointing to the math.SE question, or to migrate and leave math.SE to clean up the mess. Neither is that great, and the perfect solution would be to close as a duplicate of the math.SE question. However, if you paste the math.SE URL into the "close as duplicate" dialog, the software responds with "The duplicate question must exist on MathOverflow"

> Can we fix this, and allow closing as a duplicate of a math.SE question?