The following script shows how to reproduce the issue:

create table t (i int primary key auto_increment, j int);

-- These work

insert into t (j) values (1) returning *;

insert into t (j) values (1) returning t.i, t.j;

-- This doesn't work

insert into t (j) values (1) returning t.*;

The last statement produces the following error message:

SQL-Fehler [1051] [42S02]: (conn:5) Unknown table 'test.t'

I don't see a reason from the documentation why this syntax wouldn't be allowed, given that:

1. Unqualified asterisks are possible as per the first statement
2. Qualified column references are possible as per the second statement
3. The manual refers to select_expr being expected, without any further restrictions: https://mariadb.com/kb/en/insertreturning/