This manifests as silently not writing the content to a file.
I think this is really part of a core bug in LWP, where LWP::Protocol->collect is probably dying but that die is being discarded.
It seems like collect should maybe check if the object in $arg can be stringified and then use that as a file path. And yes, that's broken and dumb, but so is Perl 5's overloading.
But it also seems like a bug that if collect is dying (which it has to be) that getstore doesn't catch that.