Hello,
ob-plantuml encloses the body of PlantUML ( http://plantuml.com) diagram code with @startuml/@enduml clauses. Recent versions of PlantUML support non-UML diagrams like gantt, mindmap and others that needs to be enclosed with @startgantt/@endgantt and @startmindmap/@endmindmap clauses. 

I created a patch that only inserts @startuml and @enduml if the body does not already starts with the string "@start". This patch allows the execution of existing UML diagrams without @startuml/@enduml as well as non-UML diagrams that contain any @start-/@end- clause.

Regards

Henrik Koschitzki