This just started happening to me today. I must have hit some kind of hotkey to make this start happening, but I have no clue what I did.
In Foobar2000 v1.1.3, Whenever I click a track and drag it to a different spot within my playlist, it now copies the item to wherever I moved it in the playlist instead of moving it like it used to. It's driving me nuts at the moment. I can't seem to figure it out.
WTF.... I just figured it out as I was typing this. If foobar is on the second monitor, it does the copying thing. If it is on my main monitor, it moves the item like it should.
That still seems weird since I almost always use foobar on a second monitor and have never seen that behavior before.