The first Codeforces contest I authored included this problem: 1345B - Card Constructions.
Almost 2 years later, the following problem appeared in the Moldovan first state regional of OI:
Now, maybe it's just a notorious coincidence, like when a problem someone authors on Codeforces happened to appear on Topcoder before. In those cases, at least there are noticeable differences in presentation. But the author of this OI problem seems to have magically written the statement in the same way, designed the same picture, came up with the same constraints, and created the same sample test case.
Several questions come to mind. Can contestants have an unfair advantage if some have seen this problem before? Is someone being paid to invent problems for OI and steals an online problem instead? When a problem is used on Codeforces, who owns the intellectual property rights to it? Of all problems I created why didn't they steal a better one?
That's all I have for today, and don't forget to smash that like button.