I have the exact same issue. I searched before I posted, but I did not see this thread with my search.
Here are the create & alter statements used for my example (MySQL 5.0.34 with InnoDB):
create table TM (keycol varchar(36) not null, datacol varchar(255) not null default ‘x’, primary key(keycol)) type=InnoDB;
create table TMchild (rowID int unsigned not null auto_increment, keycol varchar(36) not null, childCount int unsigned not null default 0, primary key(rowID), unique key (keycol, childCount)) type=InnoDB;
alter table TMchild add constraint fkDefn foreign key (keycol) references TM (keycol);
The above definition will show in my diagram as a one-and-only-one relationship between TM and TMChild in the ERD. Even though it is really a one-to-many relationship.
Please let me know if you find a solution