When a design is posted, work locations are posted to the design's parent version even though the WorkLocation feature class has the MMDONOTPOST model name set. In normal operation the work locations should be deleted when a design is posted.
The DesignerDataset is not registered as versioned. This can be checked in ArcCatalog by right clicking on the DesignerDataset and selecting Manage. If the Registered as Versioned menu item is enabled, the dataset is not registered as versioned. Even if the WorkRequest feature class itself shows that it is registered as versioned in the Feature Class Properties, General tab in ArcCatalog, it is also necessary that the DesignerDataset is registered as versioned.
Register the DesignerDataset as versioned in ArcCatalog by right clicking on it and selecting Manage > Register as versioned. Make sure to log in as the data owner of the DesignerDataset.