This repository contains a simple reproduction for a Cargo “issue” (it's not a bug per se because exclusive features are frowned upon anyway, but that's still an): when different features are importing a different (and mutually incompatible) version of a crate, then cargo tires to find a matching version before realizing that the two incompatible versions aren't actually imported.
Depending on the selected feature, top-crate depends on dep-with-newer-version (which depends on zeroize="1.5.7") dep-with-older-version (which depends on zeroize="=1.3.0" (note the = in the version number).