When normal users vote to migrate a question to another site, after checking to see if the post author is not banned from asking questions or suspended on the destination site, the system performs multiple other checks:
- At least one tag the question uses exists on the destination, unless the destination is a meta site or at least one of its tags is on a list of "intrinsic" tags for the destination.
- Question is not an exact, word-for-word duplicate of another question, or "very similar" to another question posted by the same author within 7 days, on the destination site (designed to detect cross-posts).
...and if any of these checks fail, the migration is blocked.
However, migrations from moderators aren't subject to any of these other checks. Here on Meta Stack Exchange, as well as on beta sites, only moderators can migrate questions, so all migrations will be exempt from these checks.
Recently, a moderator migrated this question from here to Meta Stack Overflow. The same question (with exact same body, but slightly different title) had been cross-posted by the same author there a mere minute before they posted it here, and the moderator didn't notice that it had already been posted. (I don't blame them for not noticing; the question follows a common pattern of people asking Jobs questions here, since there are a bunch of these old questions from the time this site accepted these questions, and as I said earlier it was posted on MSO a mere minute before it was cross-posted here.)
Also, there was another moderator who was clueless about why a certain question that had been voted for migration by normal users was blocked. The question lacked a matching tag on the destination site, and the mod may be used to migrating these questions without issue.
Moderators bypassing the normal rules can create cleanup burdens for the destination site. In the tag case, the destination question will get the tag untagged, and the destination community will have to retag it with the appropriate tag. In the duplicate case, given that the system was recently changed to no longer mark migrations as "rejected" if they were closed as a duplicate before being deleted, the migration will still remain in place, which will result in some ill effects (e.g. users who follow links from the origin site will be redirected to a deleted question, the stub will be automatically deleted much later than it would be if it were rejected, etc.). Moderators should be aware when they're about to bypass a rule so that they can check the destination site for a duplicate, or retag the question appropriately before migrating.
Can we please warn moderators when they migrate questions if the migration would be blocked should normal users vote to migrate it, and ask them if they really wish to bypass the rule? (This request applies only to the two bullets above; I understand that the SE team may be deciding whether Q-bans or suspensions should be visible to mods on other sites, and I don't want this to conflict with that. Additionally, they won't really be bypassing the rule in that case, since moderator migrations are still subject to that rule.)
Update: After learning more about the system, it seems like this may possibly be tough to implement in the manner I'm proposing. I thus propose another alternative solution, to add in a checkbox to the dialog indicating whether or not migration rules against cross-posts or not having the same tags should be bypassed. The option should be phrased something like this:
Bypass migration rules against cross-posts and no equivalent tags
If the box is unchecked, the migration should be treated as a normal user migration, and the rules should be checked as if it were. Only if the box is checked should the rules be bypassed as they currently are.
Recently, a user had been cross-posting their question onto two sites, and a moderator of one site had been migrating their questions to the other site where they'd also asked (not the first time). As they were a moderator, the system bypassed the check against cross-posts; otherwise, the system would have likely blocked the migrations.
To be clear: this wouldn't take the place of the moderator making due diligence and checking the other site for cross-posts or equivalent tags, as the checks against cross-posts aren't 100% foolproof, but this will prevent the confusions in my original post above, and make it clear to moderators that they're bypassing rules that normal users are subject to.