ALTER TABLE ADD COLUMN returns internal error

ALTER TABLE ADD COLUMN returns internal error for DDL given in the first comment.
It is important to tell that ALTER TABLE ADD COLUMN adds the column.
debug.log contains an error that points to the fact that MDB uses offline ALTER proto under the hood first creating tmp table, replacing the original table and removing the obsolete table later. However MCS alters the table adding column in-place so MCS doesn't follow the protocol MDB expects. The error produced presumably produced by the DROP TABLE statement for the temp table created previously.