Customizing Navigator with parent entry

It seems, that puting the parent navigator entry in any other custom client file is working.
 

Seems that customizing the SrvconNavigator.client is somehow treated specially...

@Nils Wendelöv Any Idea on above ? 

Without any deeper investigation done, it do look like a limitation/defect.

 I had the same issue and noticed that this is for all customized files. The navigator entries added onto customized files cannot be interdependent. For example, I added a navigator entry on one cust client and tried to use it as the parent in another cust client, but it says the parent navigator entry is not found.

As a workaround, there were a few options which worked for me:

1. If possible move the parent and child navigator entries to one client file
   (Another issue that I noticed was that in a core file that is customized, for example Shipment-Cust, even if the entries are both in the same file we get the same error saying the parent navigator entry is not found. This issue is not there in newly created files in the Cust layer)
    
2. The other option if there are too many child dependencies, an internal link can be used instead of moving the client elements into one client file.