Thanks for your problem report @veebers!
This issue is fixed in https://github.com/snapcore/snapd/pull/6118 which is part of the 2.36 release of snapd. Unfortunately the SRU for this version is not out yet so the bugfix is not in the deb package yet. The SRU will happen today/tomorrow but it takes some days until it hits bionic-updates.
In the meantime one workaround is indeed to install the core snap even though it is not needed for the given snap. Sorry for the trouble!