Remote Buddy will choose the active Behaviour based on what application OS X reports to be the active application.

That is not always the application whose name you can read in the menu bar. Background/Helper applications running as "UI Element" can become the active application without OS X updating the menu bar or indicating this change visually.

Since the code that selects Behaviours has not been touched for years, chances are you've installed some software in the meantime that runs as "UI Element" and becomes the active application reported by OS X at the time you experience this issue.

If that active "UI element" app is not supported by a Remote Buddy Behaviour, Remote Buddy will pick the "Default Behaviour" since the active app is unknown to it.