Well, uncleV, I can't say that I understand this invisible activity stuff. I can tell you that I haven't configured any apps to auto-start, and I haven't enabled any 3D effects.
What I did just now was to go to the pager settings and un-check "Different widgets for each desktop." After doing that, each session starts off at Desktop #1. If I put the check mark back, each session starts off at Desktop #4.
But having "Different widgets for each desktop" unchecked also means I can't have different wallpapers on each desktop right? So, I don't know, I think I'd rather have sessions starting in the wrong virtual desktop.
But it does seem to have something to do with that "Different widgets for each desktop" setting.