When you buy a loan part the purchase price is the outstanding loan amount plus any accrued interest plus any premium or discount added. This accrued interest will be deducted from your interest earnings. Your Summary page will show these cash movements in and out of your account.
On the next repayment date for the loan part you will receive the accrued interest you paid for the loan parts plus any further accrued interest from the day you purchased the loan part until the next repayment date. So in effect you have not lost any money.