The issue concerns the rendering engines in Lightroom and ACR and how they differ from version to version. The concern was the lack of repeatability across versions.
According to Peter Krough, author of the DAM Book (if you don't already have it, go get it ... it's a great book), Lightroom 1 was developed on ACR 4 whist Lightroom 2 is powered by the ACR 5 engine. The problems come into play when trying to view changes made by newer versions on older software ... like trying to repeat things done in ACR 5 with ACR 4. Some functions will work and some won't. Some will repeat the results exactly and some won't.
When performing our kind of work, it's important to list the equipment and software used, including version and/or build numbers. In this way, others can create the same scenario that exists in your lab before attempting to repeat your results.
Keep the questions coming. And, as always ... thanks for reading.