Copyright claim mysteriously removed

[The NotARubicon!]

I created a video using music that I knew was copyrighted and when I uploaded the video it was immediately flagged by ContentID and monetized by the copyright holder. I knew this would happen and was OK with it because I knew it would be a popular video.
Today I was browsing through my Video Manager and noticed that the copyright claim was no longer there and I was able to activate monetization for the video.

I've never seen a copyright claim removed like this before. Is this normal/anyone see this happen?

 

[KatyAdelson]

I have had a copyright claim eventually be retracted, but I had also tried (and failed) to dispute it, so maybe that's why. I once got a copyright claim for playing a public domain song written hundreds of years ago. The copyright holders thought I had just used a version of the song that they recorded, but it was actually my own version... I immediately disputed the claim when I saw it was flagged, but they rejected my dispute!! I was like "omg! wth!?" but I was also a new channel at the time, so I was scared to escalate it to the next level (I saw that you had to share your address and whatnot with them to dispute it again). About a year later, I noticed that they finally removed their copyright claim.

My story is a little different because I was using public domain stuff, but it taught me that copyright holders can retract their claims. I'd search through YouTube's music policies to find your song to see if they've changed any of their rules recently:
https://www.youtube.com/music_policies