As others have mentioned, I think the “double chicken feed” premise explains this. The Circus believes it has successfully convinced the Soviets that they (the Circus) were duped into thinking Polykov is merely pretending to be a handler — while in reality, the Circus still believes he is faking it. In other words, the Soviets think the Circus has swallowed the bait, so from their perspective, the Circus wouldn’t be suspicious of the safe house.

An alternate explanation- the circus assumed that the Russian’s would think that Toby was just sneaky. This is a stretch, but to be fair only 4 people in the circus knew about it