There are some changes pushed to source today that improve the GUI performance when scrolling. The more composite columns you have, the more the improvement. It does this by not processing a book for details display until the selection hasn't changed for 100ms. As a result, the book details display(s) update 100ms after scrolling or paging stops.
It also changes the semantics of db.get_metadata() (not ProxyMetadata()). Composite columns are now evaluated when they are used instead when get_metadata() is called. I checked to be sure it worked in all places where calibre uses get_metadata(), but it is possible that some plugins do things that "go around" the rules by reaching inside a metadata object in ways we don't expect. This is the reason I hope people can run it, as there is no way I can simulate how people use which plugins.
