For the following command an error is shown and it is formatted incorrectly. (The blanks are inserted by the code formatter).
ALTER SESSION CLOSE DATABASE LINK hq.acme . com;
[Error] Syntax check (13: 43): ERROR: line 13, column 43, ending line 13, column 43: Found '.': Expecting: end-of-input -or- ADVISE CLOSE DEFAULT DISABLE ENABLE FORCE SET SYNC
However, it is executed correctly (after the blanks are removed) with both F5 and F9, if that makes a difference.