Not quite sure why they would be referred to as 'Slave Bonds' Offshoreigor?
The bonds that I am familiar with don't involve any payments from the trainee during the bonded period, they are only an agreed notional (and usually reducing sum), to cover the costs of training and only become serious cash if the trainee/employee leaves before the agreed period is up.
As Bealzebub has pointed out, quite clearly, they are a simple contract between employer and employee/trainee to ensure that the employee gets a reasonable return on their investment in an individual, they don't restrict movement, (slaves were restricted). An employee is free to go anytime, just so long as they honour their contract and pay for any outstanding balance of their training costs as they agreed to when they joined.
I know of a few people who have 'jumped ship' and been successfully sued by the employer, in the employees home country, for the balance of bond, and quite a few others who visited the office and came to an amicable agreement over the final sum and method of payment.
The bottom line is, if you accept the deal you should expect to honour it.