As you already have it working, that answers my question. Thanks.
Here in the UK, bats are a protected species, and it is quite illegal to use any device that interferes with their hunting and feeding processes. So I guess that's why I've never come across it here.
I have built several bat detectors over the years, and find it interesting to monitor and record their ultrasonic echolocation calls. The reason I suggested that additional ultrasound might not affect them is because I have always been amazed that they appear to be able to navigate - and hunt - using ultrasound in the presence of loads of other bats doing to same thing. And they appear to be able to ignore all 'received' ultrasound apart from their own.
Still, if you have enough 'noise' interference from an external source, I guess it could confuse them. And your experiments seem to confirm that is the case.