Problem solved 🙂
Some DeviceInfos working only with "modern browsers". This depends on the user-agent of the calling client. WCF doesn't send an user-agent by default so it's not a "modern browser" and some DeviceInfos are ignored. This fact doesn't seems to be documentet anywhere 🙁
The solution is to write an endpoint behavior for the WCF Service which sets the user-agent for example to IE 11 (which is a modern browser for SSRS 🙂 ).