Has anyone else experienced LR 2.0 rendered previews at 1:1 being discarded if any changes in Develop have been applied and LR then relaunched. It doesn't happen in LR 1.41. Automatically discard 1:1 preview settings are set to Never in Catalogue settings File handling dialogue box. MacPro 2 x 2.66GHz 8GB ram 10.5.4. It does this whether or not writing to xmp is applied. I haven't tried, as yet, deleting preferences file but will report back if that is successful.
John