deleting projects not working if build-results exist

If build-results (failure or success) exist, then the project doesn't get deleted. The following error's occur:

javax.jdo.JDODataStoreException: Delete request failed: DELETE FROM `PROJECT` WHERE `ID` = ? NestedThrowables: com.mysql.jdbc.exceptions.jdbc4.MySQLIntegrityConstraintViolationException: Cannot delete or update a parent row: a foreign key constraint fails (`continuum/BUILDRESULT`, CONSTRAINT `BUILDRESULT_FK3` FOREIGN KEY (`PROJECT_ID_OID`) REFERENCES `PROJECT` (`ID`))

or

javax.jdo.JDODataStoreException: Update request failed: UPDATE `BUILDRESULT` SET `BUILD_DEFINITION_ID_OID`=?, `BUILD_NUMBER`=?, `END_TIME`=?, `ERROR`=?, `EXIT_CODE`=?, `MODEL_ENCODING`=?, `PROJECT_ID_OID`=?, `START_TIME`=?, `RESULTSTATE`=?, `SUCCESS`=?, `RESULTTRIGGER`=? WHERE `ID`=? NestedThrowables: com.mysql.jdbc.exceptions.jdbc4.MySQLTransactionRollbackException: Deadlock found when trying to get lock; try restarting transaction

After deleting all build-results, the project can be deleted.