Thanks cfor for the hint with the API.
Unfortunately we do not use the API. Our vCD is kind of a self-service platform for all engineers (about 100) in our company, so the API is not a solution for us.
I have an update on this from VMWare support:
Seems that a fix for this will be included in next patch 5.1.3 and also in vCD 5.5.
Will keep you up to date.