I read your post about the work ethic problems. I'm sorry that is happening to you. They should not be shifting the blame to you. Maybe this happens a lot where you work and maybe that's why they keep shifting you around, so they (the ones not working) are not "exposed".
A friend of mine works with people that disappear for hours also. Another one watches tv ... leaves early yet is paid ft status. It is not good for company morale to have this going on but it happens a lot from what I hear.
Def. keep a log (at home of course) and document events as they happen. Names, dates, times.