When listPackages is called without a tagID, userID, or pkgID option, it performs a fundamentally different query than it does it the other cases. This case was split off to the listPackagesSimple function in #223, but the polymorphic behavior goes back to the very beginning.

In the simple case (no tagID, userID, or pkgID option), the call simply queries the package table. This will show all packages in the system. However, when any of these options are given, the call will query the tag_packages table, showing only packages that are included in some tag.

This can lead to the confusing situation where a call to listPackages() shows a particular package, but a call to listPackages(pkgID=N) for said package reports no results.

As this is very longstanding behavior, I'd be hesitant to alter it. However, it is worth clarifying in the docstring.