Unique Constraint in sqlite does not always raise IntegrityError

I am using Python's sqlite3 wrappers:

I have a table that I create using:

CREATE TABLE IF NOT EXISTS patientsname (id INTEGER PRIMARY KEY AUTOINCREMENT, original, cleaned, study INTEGER, UNIQUE(original, study), FOREIGN KEY(study) REFERENCES studyinstanceuid(id))

If I try to insert multiple time for the same (original, id) I usually get:

IntegrityError: UNIQUE constraint failed: patientsname.original, patientsname.study

every once in a while I get (I have seen on OSX):

OperationalError: UNIQUE constraint failed: patientsname.original, patientsname.study

and seen on Linux:

DatabaseError: UNIQUE constraint failed: patientsname.original, patientsname.study

What is the correct way to catch the unique constraint violation?