I voted to migrate this question to physics.SE, as three others had done before me. I expected that it would be migrated once a fifth vote was cast, but when I checked on it I was suprised that it said "closed as off topic" instead, the title had "[closed]" and not "[migrated]" in it, and I wasn't redirected to phyiscs.SE; in other words, the question behaved in every respect as if it had been closed and not migrated. Since this made no sense, I checked on physics.SE, and indeed the question is there and is marked as both migrated from math.SE and closed as too localized. Leaving aside the wisdom of closing this question as too localized, apparently by the vote of a single moderator (I wouldn't want that to happen on math.SE), note that the close reason is different from the one given on math.SE. It seems that the question was first migrated, then closed as too localized, and this somehow confused math.SE into thinking that it was closed as off topic.
That is intentional behaviour. If a migrated question gets closed or deleted, the migration is rejected. This removes the link from the source site to the target, and closes the question as off-topic.
This makes it much easier to reverse bad migrations, as you no longer need the moderators of both sites to coordinate it.
Some things to consider when voting for migration...
- Physics.SE is less tolerant to "do my homework" posts than Math.SE. Not saying that their approach is better or worse, just a matter of fact.
- While "native" questions may be fixed after closure and then re-opened, migrated questions do not get a second chance (per the answer by Mad Scientist). If the receiving site is not happy to receive it, that's the end of the story. So it has to be a good question to begin with. Which brings me to
- The Golden Rule of Migration
I think people here on math SE should be very very careful concerning migrating questions to Physics SE. The rules and policies concerning what is an allowed question on Physics SE, are very different and much much more restrictive than what I observe here on math SE (where I admittedly have hanged around less often so far).
Whereas here on maths, people seem to look for anything good in every question and let them be answered if possible, on physics SE questions get often closed for "political reasons" ("they are not a good fit for the physics SE site" according to the MSO definition), even though they could easily be answered by the people, many people like them, and knowing the answers would be helpful and useful to many people seriously interested in learning physics.
An example of what I mean is for example this meta post and the corresponding discussion in the answers and comments.
So I would give the advice to refrain from migrating questions from here to Physics SE, if the probability for them getting a satisfactory answer here is not negligible.