BC break when using custom separator in Class diagram

Hello. Since PlantUML v1.2026.7 I have an error generating Class diagrams.

@startuml
set separator \ 
!pragma useIntermediatePackages false
skinparam linetype ortho
skinparam MinClassWidth 140
hide circle
hide empty members
!theme _none_
class App\Entity\ImageRequest {
+ id : ?int = null
+ user : ?string = null
+ max : ?int = null
+ columns : ?int = null
+ size : ?App\Model\Image\SizeEnum = null
+ createdAt : ?DateTime = null
}
@enduml

This should be the output from the previous code:

Instead, this is the error message I got:

  Error Output:
  ================
  ERROR  1
  Syntax Error? (Assumed diagram type: sequence)

The offending line is "set separator \ ", note there is an empty space at the end of the line.
I tried to fix this using double backslash, but then the separator is simply ignored.