No idea, Lefty! It's not my design
But the test itself has been unchanged for years... I can only assume those who designed the setup know what they're doing.
The sounders don't actually come with seal tabs on them (which seems odd, as all the ones I've actually bought came with them and I don't normally pull them off until I'm done with them). If the IPA has done something horrible to the innards then I suppose there's little I can do other than apologise and make some more...
I wonder, is it worth opening one up completely to investigate any possible internal damage? We've got thousands on the shelf so I could compare a new one to one that I've molested to see if there's any difference.