Charles Watts-Jones wrote:No in that I didn't trash the current version …, I just tried to instal over it which is my usual practice with upgrades.
That's where you ran into trouble.
QRecall installs several components and a background processes, some of which are contained in the application bundle. This means that the application bundle contains resource files which are always in use. Attempting to replace the existing application with the new one fails, because the Finder refuses to delete the files that are active. You end up with a half-deleted/half-installed version of QRecall.
Normally, you'll never encounter this. The initial installation is immune, and upgrades are handled automatically by a process that first downloads the new version, sets the old one aside, starts the new version which uninstalls the resources open in the old one, and then safely removes the old version.
Manually switching from a release version to a new beta is where some care must be taken.
(in my defense I'd add that I had never read that page before)
That's because, until this second beta, no one — except maybe myself and a few testers — has ever needed to install a new beta over a released version.