So for whatever reason I was going through stackoverflow looking for questions that had slipped through the retag/migrate net. I found this question, which clearly didn't belong on SO, and probably would be migration-rejected here due to low quality; however, I can't custom-close-vote (not enough rep), and flags don't have a custom option. I flagged it for migration in the hope that it would be processed correctly.
I then came across this question, and decided to use the same tactic -
No, I haven't! (Apologies for the poor freehand-circle quality; the Surface RT is not very conducive to drawing them.)
Have I done something wrong and been covertly banned from raising close flags? Is there a new one-outstanding-close-flag limit? Is there a new no-more-close-flags-while-you-have-an-outstanding-migration-flag limit? Is this just a plain old bug?
Update: Turns out I flagged it two weeks ago, and the flag was still waiting for review. *facepalm*