You don't pay interest on interest ever. Unpaid interest and principal balance are kept in two separate buckets and interest is only calculated on the principal.
The only way you'd ever end up paying interest on interest (on a fixed home loan loan) would be if you and the lender both agreed to rewrite the loan. In which case any unpaid interest from the original loan would be combined with remaining loan balance to form the basis of the new loan.
That said, I have seen cases where the borrower fell a single month behind, and remained a month behind, and ended up making payments for more than a year without a single penny going toward principal.
Yeah... no interest on interest... there's that nasty bong charge called a late fee which is worse.