I'm working on reliably identifying devices attached to computers and it seems that a single call to this function, from any of the apps which try to identify devices, mean that InstaCal is ignored until I reboot the computer.
If that's an accurate understanding, I can either write all my apps to use Instacal, or have none of my apps use instacal.
But if there's an "use_instacal()" function then I can decide on an app-by-app basis.