Documentation issue, or perhaps just a local mode issue in general

Hey y'all,

I've been working on customizing some Jetpack expected behavior, and while doing so in local mode, have come upon an issue I think is worth starting a conversation about.

Basically, when local dev mode is turned on, it appears Jetpack has potentially unexpected behavior as to what it's active status/modules are.

The following gist is a modified version of your Related Posts documentation for customizations on the Jetpack website:

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Start with the Related Posts documentation and the local-mode behavior described in the issue. Examine how Jetpack_RelatedPosts and JETPACK_DEV_DEBUG interact, then document the relevant active-module checks and local-mode expectations; done means the guidance clearly explains what users should check and why.

Written by the indexing model from the issue text.