This is weird. Could you turn trace on using the following diagram:
@startuml
!pragma svek_trace on
[A] - interface
[B] ..> interface : use
@enduml
With the pragma directive, two "svek.dot" and "svek.svg" files will then be generated in your current directory.
Could you send both of them by mail to plantuml@gmail.com so that we investigate this ?
Thanks,