Thanks for passing this along.  I’ll document and send along to the product devs. 

There might be a workaround.   
1. Make the option source for the reference field be a model  (Call it model X). 
2. Add a model action that fires when the the client field is updated. 
3. This action should pass value into a condition on Model X and the requery it. 

Finally, you may have to refresh the editor that shows the picklist field - and this would take some javascript.   

Hope that gets the ideas flowing…