Repentant thieves

The thieves who returned vessels are believed to say "We did not touch those vessels" (and the vessels are therefore pure).

But we learned, the thieves who entered a house, everything in the house is impure (and the vessels). No problem - first case is about the thieves who repented. Indeed, this is why the first case says "returned the vessels".

Chagigah 26a.

How often does it happen?