Track Stand, Matched Third Party Content

I've been working on an arrangement of a Vivaldi piece over a few years - finally got something listenable and posted it on youtube. Now youtube's comment on my page is:

3:29 Track Stand, a piece for electric strings an… HD
January 20, 2012 5:19 PM
Matched third party content.

http://www.youtube.com/watch?v=vykFpTsuoeA 

Clicking on the link to find out who this third party is shows:

1980

Your video, Track Stand, a piece for electric strings and drums , may include content that is owned or administered by this entity:
Entity: Music Publishing Rights Collecting Society Content Type: Musical Composition

So, let me get this straight...a piece composed by Vivaldi in 1711 was later arranged for organ by Bach in mid 18th century, then about 250 years later I arranged the music for 2 electric guitars, 12 string bass, and drums, and the  Music Publishing Rights Collecting Society claims they own the copyright?

The Entertainer, c. 1980 Art Sulger

They did this for a few other music videos of mine. They have a facebook page. Their alleged company statement sounds like a parody page some other disgruntled musician created. Though lately I have trouble separating the parodies from the reality:

Founded 2005
About You get the pleasure of posting videos
We get the pleasure of making money from your videos
It's a win-win situation :)
Company Overview We are the Music Publishing Rights Collecting Society. In other words, we are a society that collects rights from the publishing of music onto sites like YouTube.
Mission Our mission is to file copyright claims so that ads will be placed onto certain videos, and we will be able to make money off of them. We do not seek to have anyone's videos blocked in certain countries or disabled altogether, all we are trying to do is make a bit of money. That's not so bad, is it?
Products A wide variety of people post videos containing content that belongs to our organization. We didn't make the music ourselves, but nonetheless we can still make money from it. 

In any case, click on the link - the video and music is nice. I used software from Music Animation Machine to make the notes display. If you're interested, you can download the software for free from the creator's page. Video editing (syncing the display to the playing was tedious - linux and windows don't seem to agree on tempo) is via Openshot, and the sound processing is via Audacity.