Sharepoint 2010 Document library file disappears

I have an interesting problem. Occurred only today, never seen this before.
I have a separate document library for weekly reports. Inside this library I have folders in which I have the actual documents. Now the documents are moving on their own to the upper level of this document library folder! 2 of my documents came out from 2 folders to the document library level.
Has anyone else had these kind of problems? is this just a bug on the  sharepoint Team Site or should I get worried about this?
I’m able to move the documents back to correct folder (using the Open with Explorer + Cut & Paste) but as soon as I edit those again the location is changed.