Hello,
Please look at this simple script:
@startuml
foo -[plain,thickness=16]-> bar1: [plain,16]
foo -[dashed,thickness=16]-> bar1: [dashed,16]
@enduml
It is working in the editor we correctly get two thick lines:

While if I render this using the `plantuml.jar -gui` I get the plain line in its thin thickness.

It seems there is an issue with the plain line as every other style works...
Can anyone else reproduce this?
Thanks,