Client Lib/support functions not loaded in production

I normally use a server, client, lib folder setup for projects, without the isClient/isServer. Files in /client works just fine in debug, but when uploading to production using mup, the files are not run upon client load.

Putting it in /lib and using isClient-wrapper works fine.
Putting it in /client with or without wrapper does not work at all.

Is it the load order in production that messes it up? Some sort of undefined behaviour, or simply a bad bug?