あとで見たら板がほんのちょっと引っかかってるだけ(数ミリ程度)な作りだったので、逆によくこのときまで耐えてたなと思いました。
大家さんに直す旨伝えたらそのままでいいと言われたので助かりました(^^;)

I checked afterward, and found it happened because the board had been built so it was just barely supported (as in by a few mm), so I was actually amazed it had held up as long as it did. I conveyed my intentions to fix it to the landlord and was told I could leave it as-is, which saved me the trouble. (^^;)