I have 10.4.5326 (97a2e75) installed and setting the default profile is not working. I have tried cycling which profile is default and I have tried different combinations of quitting out of different profiles - in all cases eM Client always opens the same profile. It appears to choose the profile alphabetically.
Additionally, if I set eMC to show the profile picker at startup, it still opens the “not-default” profile and it shows the profile picker.