Change not persisted: edit the user name and then close the Doc Settings, i.e. not explicitly set the edit but merely shift input focus.
Change persisted: edit the user name and press Return to set the edit.
The latter is normal behaviour in many aspects of Tinderbox, e.g. column view editing, so isn’t a bug per se. This behaviour in column view trips me up regularly, but it is how the UI is designed.
Just to confirm Mark A’s response, this is an aspect of TB’s design that requires being aware of. In a number of dialogs, you might expect that the signal for completing an entry and being ready to move to the next field is, exactly as you put it, that the field loses focus. For instance, you might just click over to another field.
But in fact in many TB dialogs you must hit the Return key to signal that the entry is complete and you want it to be accepted. I don’t have a complete view of exactly when Return is needed and when not, but if you ever find values not sticking, try Return as the first possibility. For me that generally does the job.