In version 7966, we have added back this "old" syntax for "Activity Beta".
The goal is not to support this "old" syntax forever, but to allow people to use the last versions of PlantUML and let them slowly migrate their diagrams. Having a version that support both version will help for this task.
Note that we are not talking here about the actual syntax (http://plantuml.sourceforge.net/activity.html
), which will remain probably forever.
Thanks to post here if you find other issue about this.