I have noticed the same behaviour (v.18.104.22.168) plus the ctrl+space command only intermittently works for looking up column names from a table alias.
ctrl+space command also does not always work
It's all about context. The parser needs a valid SQL or PL/SQL statement to be able to make these types of things work.
Please give code examples, using common objects like SCOTT or DD views to explicitly describe your problem.
Here's a quick example using data dictionary tables. It sometimes works (if the query has been parsed?), sometimes doesn't, and sometimes I can get a list of columns for an alias (e.g. zzz) that isn't defined:
select * from
(select object_name from all_objects a
where A.CREATED = 'a') b
, (select status from all_objects c
where A.DATA_OBJECT_ID = 1) d
There may be several other scenarios - e.g. cursors in a package.
I can reproduce for "select object_name from all_objects", when Ctrl+click the table "all_objects",no response, but Shift+F4 is fine. Filed bug to trace.