Comment (by Roland Haas):

This will happen with every ExternalLibrary. It does not hurt though to repeat the information in each thorn’s documentation.tex (and the UsersGuide). The easier it is for this to actually be found (rather than pointed out after the fact) the better.

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Ticket URL: https://bitbucket.org/einsteintoolkit/tickets/issues/2428/possible-issue-between-externallibraries