This is reproduced by running MultiCircleJpaCascadeIdentityTest or MultiCircleNonJpaCascadeIdentityTest on Oracle databases. Looks like the Oracle JDBC driver contains a bug:
This occurs when the driver is attempting to parse the table name from an INSERT query where the inserted table name contains just one character. If you rename the entities related to the two mentioned tests so that they will have more than one character, the tests will pass.
I suggest that we add a workaround for this in our TS (so the tests don't fail) and report this to Oracle.