don't look to close, it might change the results

We all know, if we try to look to close on some details, the results we get may change from the original observation.
This is also sometimes true for Oracle Trace events:
During analyses of a query with XMLTYPE which fails with ORA-12850 (in a 4 node RAC DB), Oracle Support asked for some trace files. the query itself is something like

SELECT XMLTYPE(
CURSOR( SELECT ...
FROM gv$lock l
JOIN gv$session s
... ) )

and the original error is

ORA-19202: Error occurred in XML processing 
ORA-12850: Could not allocate slaves on all specified instances: 4 needed, 1 allocated 
ORA-06512: at "SYS.XMLTYPE", line 343 
ORA-06512: at line 1 

But with a specific trace event:

alter session set events 'trace [SQL_Compiler.*] disk highest'; 

the error changes to

ORA-19202: Error occurred in XML processing 
ORA-00918: column ambiguously defined 
ORA-06512: at "SYS.XMLTYPE", line 343 
ORA-06512: at line 1 

As there are 2 different Errors now Oracle Support has more to analyze 😂