If it was very recent then it most probably means the Item.Update() method has triggered your event.

If it is not a very recent date then it most probably means the Item.SystemUpdate() method has triggered the event.

SystemUpdate method avoids SharePoint 2007 to change modified date and modifier fields. Argument false tells that no new versions are expected. SystemUpdate solved my problem perfectly well.

file.Item.Update() //fails miserably on ItemChanged due to the SPCheckOutStatus.ShortTerm lock.
file.Item.SystemUpdate(false); //This works while the user still has the document open.