I've purchased, downloaded, installed Photoshop Lightroom 4.0 on OS X Lion 10.7.3 and have encountered a bug. With a folder containing keyword tagged images selected, I choose the "metadata" library filter in order to find images via keywords. Consistently, nothing shows up in the search results panel when any individual keywords are selected. When "All (...)" is selected, all images show in results. Any individual keyword, or multiple selection thereof, fails to produce results. This occurs with any combination of other filters applied.