Thus, the cloning process as the LDAP user (did not want to store the foreign username/password explicitly in the galaxy user files) worked, although I get this message:
"*** failed to import extension hgext.imerge: no module named imerge"
(once at the process' beginning and once at the end)

Anyway, this seems to be more a warning than an error. I found possibility to silence it, but would like to understand what the missing may cause.

Any clue, anyone?