Be aware that pg_fetch_all() is subject to the same limitations as pg_fetch_assoc(), in that if your query returns multiple columns with the same name (or alias) then only the rightmost one will be returned in the associative array, other ones will not.
A simple example:
$res = pg_query(
"SELECT a.*, b.* -- Fetch all columns from both tables
FROM table1 AS a
LEFT OUTER JOIN table2 as b
$rows = pg_fetch_all($res);
In this example, since we're selecting columns via *, if any columns from table2 share the same names as those in table1, they will be the ones returned despite that table2 (as the optional side of an outer join) may return NULL values.
This is not a bug, just a limitation of associative arrays in general, and is easy enough to avoid by structuring your queries carefully and using column aliases to avoid confusion.