Duplicated metadata in PNG?

Question

Environment: Windows 10, Java 1.8.0_241, PlantUML version 1.2020.22 (also reproduced it with V1.2021.0)

Initially met it in VS Code + PlanUML extension, also reproduced it in command line (java -jar plantuml.jar)

Steps to reproduce:

1. Create sequence diagram
2. Export diagram to PNG
3. Use 'Extract PlantUML Diagram Source from Image' on file from step 2.

Expected result:
Diagram can be extracted and result matches initial diagram

Actual result:
Initial diagram can be extracted, but data is duplicated (extracted/displayed twice)

Comments

I also see duplicate metadata in generated SVGs, here is my minimal example. The issue is caused by having a comment in the file, this UML when generated as a SVG includes duplicate metadata. If you remove the comment, the duplication goes away:

@startuml
'merge
a -> b
@enduml

I've verified this locally and on the online server (using "View page source" you can see the issue is the diagram is recorded once with comments, then once without)

@startuml
'merge
a -> b
@enduml

@startuml
a -> b
@enduml