Right now psycopg2 is required to be exactly version 2.6.2, which makes it mostly impossible to install pgadmin4 without having the postgresql C development packages installed (since you need to rebuild psycopg2 from source to make that work, given that few platforms ship *exactly* that version).
There are a number of cases where queries in both pgadmin4 and pgadmin3 are done against pg_depend but falis to constrain the query on classid.
In particular, if for example a constraint and a sequence exists with the same oid (which is perfectly valid, as they are in different tables), a column will suddenly refer sequences that are completely incorrect. When we look up sequences, we have to make sure we only match dependencies against pg_class.
Magnus Hagander