I have been having this problem since yesterday. I went through everything that was suggested, the clear cache, the rebake the relog, I am no Newbie, I have been in SL a long time, and even tried a few tricks that were not mentioned like handing off the items to an ALt av, and seeing if it affected them as well. and the answer was yes.
The quick fix for me, was to get an older version of my video card driver.. which I had upgraded 2 days ago .
The Card is an Nvidia GFORCE 8500 GT - I upgraded as always to the latest driver when it came out ... I just rolled it back to 175.19 version and that seems to have fixed the issues, it might not be an undocumented feature with SL but a bug with the card driver .